There won't be a two front Sino-Pak vs India scenario. One thing we keep discounting in the Sino-Pak vs India scenario, is the Saudi factor.
Couple of things,
India has the worlds second largest standing army, nuclear armed, we don't need any direct support, we have enough to make Pakistan+China regret any misadventure.
Secondly, USA will not let India go down just like the that. USA sees India as a hedge against China. Although it depends on the motive and the objective of the so called two front war. If its just quick territory grab, then USA might just sit back and reap the benefits of a real pissed off and anti-China India post war.
However, if the motive of the two front war is more than territory grab, then USA will definitely put pressure, not on China but Pakistan. Whether Pakistanis like it or not, Americans still command a considerable amount of control over Pakistani foreign policy. If not direct control, then control via Saudi Arabia. The same goes in a Sino+Pak Vs America scenario, one religiously packaged statement from the Saudis will make Pakistan switch camp, if not then at least cause internal strife within Pakistan and its military.
Thirdly, Russian factor. Russia will help India covertly, cause Russia too fears a belligerent China with lot of its far eastern territory will come under direct threat from China in the future. Keeping China in check will help its cause.
Israel will help as much as it can, specially if it can achieve the neutralization of the Islamic bomb. However it won't go against the wishes of America.
France will definitely help with weapons and such, covertly mainly.
UK would sit back and enjoy the show.
Nepal and Bhutan will help India in their own capacity.