We don't marry sisters and cousins here unlike Pakistan-
https://www.dawn.com/news/1323037
https://truthabouthinduism.wordpress.com/2014/12/27/hinduism-and-lust/
Incest
As per Brihadaranyaka Upanishad all creatures were born after God raped his own daughter,
Birhadaranyaka Upanishad 1.4.3-4 ”He was not at all happy. Therefore people (still) are not happy when alone. He desired a mate. He became as big as man and wife embracing each other. He parted this very body into two. From that came husband and wife. Therefore, said Yajnavalkya, this (body) is one-half of oneself, like one of the two halves of a split pea. Therefore this space is indeed filled by the wife. He was united with her. From that men were born. She thought, ‘How ccan he be united with me after producing me from himself? Well, let me hide myself.’ She became a cow, the other became a bull and was united with her; from that cows were born. The one became a mare, the other a stallion; the one became she-***, the other became a he-*** and was united with her; from that one hoofed animals were born. The one became a ewe, the other became a ram and was united with her; from that goats and sheep were born. Thus did he project everything that exists in pairs, down to the ants.” Tr. Swami Madhavananda
Adi Shankaracharya writes on this verse,
‘’He, the Viraj called Manu, was united with her, his daughter called Satarupa, whom he conceived of as his wife. From that union men were born.’’ by Shankara on Brihadaranyaka Upanishad 1.4.3, Shankara Bhashya, p.101, Tr. Swami Madhavananda.
Samba was the son of Krishna born to his wife Jambavati. Krishna’s sixteen thousand wives were sexually aroused seeing their step son Samba. So Krishna in anger cursed his son.
Varaha Purana 177.2-31 “When Krsna was living there with his wives and sons, once Narada stepped in…But Narada took Krsna aside and spoke to him in private. ‘I have to tell you something in secret. Please liten. Your son Samba is young, eloquent and handsome is longed by all the women here. The Supreme God gave you these sixteen hundred divine women for your pleasure. Their minds get agitated (with love) when they see Samba, and this (scandal) has spread even in Brahmaloka…By calling Samba and all this multitute of women and seating them here, I shall show you whether what I say is true or false…Then Samba entered with folded hands and waited to know the command (of Krsna). Seeing the exceptionally handsome Samba, all those noble women felt agitated in mind even when Krsna was watching them. Then Krsna asked these beloved women of his to get up and go to their homes and they did so… Looking at Narada, Krsna bent down his face in shame. He then told Narada in detail about the nature of women and their conduct leading to sin. ‘They have no consideration of time, of secrecy of what they do. Still they pass to be virtous. Women irrespective of their age, whether they be girls, teenagers, middle-aged or advanced in age, get their passion excited at the sight of a handsome man. O great sage, this is natural to them… A chariot does not move, ‘ (he said), ‘with a single wheel alone. It is only with the response of men do women get excited with passion. They get gratified by the looks of men. Seeing (your other son) Pradyumna, they become highly shy. But by seeing Samba, they become stricken with passion and the sandal paste and such other things (on his body) act as additional excitants. So Samba must be held responsible for ruining your women and you cannot obliterate the scandal that has reached even Satyaloka…Krsna then cursed Samba to become ugly and immediately he became a leper. Foul smelling blood began to ooze from his body which became full of wounds.” Tr. Venkitasubramonia Iyer, J.L. Shastri
There is another version of this story,
Matsya Purana 70.2- “Siva said:- There will be 16,000 wives of Krisna in the Yuga mentioned before. When once, in the spring time, those ladies, having decorated themselves with ornaments, would be drinking together on the banks of a pond studded with full budded lotus flowers, dancing with the wind and resounding with the melodious notes of the cuckoo and musical tunes of the big black bee, they will see Lord Samba, beautiful like Cupid, having eyes handsome like those of a gazelle, and wearing the garlands of malati, passing by. They will cast on him amorous glances, their hearts being fired with lustful feelings and they being targets of the arrows of Cupid. Lord Krishna will come to know all that with his mental vision, and will curse them as follows: ‘Because you cherished the desire of amorous pastime during my absence, all of you will be taken away by bandits.” Tr. Taluqdar of Oudh, edited by B.D. Basu
During propagation of living beings, Manu sprang from lower half of Brahma and Satarupa from left hand side of Brahma’s body. And these two siblings then begat couple of children,
Devi Bhagavatam 3.13.15-16 Next Svayambhava Manu sprang from the lower half of Brahma; and the daughter named Satarupa came out of the left hand side of the Brahma’s body. The two sons Priyavrata and Uttânapâda were born of Manu in the womb of S’atarûpâ and the three daughters, very beautiful and fair complexioned, were also born of him.
Another version shows that when Prajapati created sons and a daughter from himself his sons were attracted to their sister and out of desire they discharged semen which Brahma preserved it in a bowl
Kausitaki Brahmana 6.1.1-12 “Prajapati, being desirous of propagation, underwent penance; from him when heated were born five, Agni, Vayu, Adityaa, Candramas, and Usas as fifth. He said to them, ‘Do ye also practise fervour.’ They consecrated themselves; then when they had consecrated themselves and had acquired fervour, Usas, offspring of Prajapati, taking the form of an Apsaras, came out in front of them; to her their minds inclined; they poured out seed; they went to Prajapati, their father, and said, ‘We have poured out seed; let it not remain here’. Prajapati made a golden bowl, an arrow breadth in height and similar in breadth; in it he poured the seed; then arose he of a thousand eyes, of a thousand feet, with a thousand fitted (arrows).” Tr. A.B. Keith
Hindus views marriages with cousin as incesteous, but Krishna himself is said to have married his paternal aunt’s daughter. Mitravinda was the daughter of Rajadhidevi who was the sister of Krishna’s father Vasudeva making Mitravinda the first cousin of Krishna,
Srimad Bhagavatam 10.58.31 “My dear King, Lord Kṛṣṇa forcibly took away Princess Mitravindā, the daughter of His aunt Rājādhidevī, before the eyes of the rival kings.” Tr. Swami Prabhupada
Krishna is said to have married another cousin named Bhadra,
Srimad Bhagavatam 10.58.56 “Bhadrā was a princess of the Kaikeya kingdom and the daughter of Lord Kṛṣṇa’s paternal aunt Śrutakīrti. The Lord married Bhadrā when her brothers, headed by Santardana, offered her to Him.” Tr. Swami Prabhupada
Srimad Bhagavatam 10.83.15-16 “Śrī Bhadrā said: My dear Draupadī, of his own free will my father invited his nephew Kṛṣṇa, to whom I had already dedicated my heart, and offered me to Him as His bride. My father presented me to the Lord with an akṣauhiṇi military guard and a retinue of my female companions. My ultimate perfection is this: to always be allowed to touch Lord Kṛṣṇa’s lotus feet as I wander from life to life, bound by my karma.” Tr. Swami Prabhupada
A story in Mahabharata says that after Asura Ilwala killed the pitrs of Rishi Agastya, they requested Agastya to beget a son that would save them from the pit (hell). As requested by them Rishi Agastya first creates a girl with an intention of marrying her. Logically this makes her the daughter of Rishi Agastya. After creating her, Rishi Agastya gives her to a childless king who was performing penance to obtain progeny, and the king adopts the girl child who was named Lopamudra. After reaching the proper age fit to beget a child, Rishi Agastya marries her and begets a child,
Mahabharata, Vana Parva 3.96 “…Agastya replied, saying, ‘Ye Pitris, I will accomplish your desire. Let this anxiety of yours be dispelled.’ And the illustrious Rishi then began to think of perpetuating his race. But he saw not a wife worthy of him on whom he himself could take his birth in the form of a son. The Rishi accordingly, taking those parts that were regarded as highly beautiful, from creatures possessing them, created therewith an excellent woman. And the Muni, endued with great ascetic merit, thereupon gave that girl created for
himself to the king of the Vidharbhas who was then undergoing ascetic penances for obtaining offspring. And that blessed girl of sweet face (thus disposed of) then took her birth (in Vidarbha’s royal line) and, beautiful as the effulgent lightning, her limbs began to grow day by day…” Tr. K.M. Ganguli
Mahabharata, Vana Parva 3.97 “…And at these words of his daughter, O monarch, the king gave away Lopamudra unto the illustrious Agastya with due rites. And obtaining her as wife…” Tr. K.M. Ganguli