The US will not intervene in the territorial disputes on the behalf of VN and PI, especially if China is not the aggressor and China won't be one. All China has to do is to hold the present status quo and in a few years the SCS will be swarmed with Chinese warships, by then it'll to late for anyone, including the US (not worthwhile) to put up a fight.
For now the PI has no wherewithal to be the aggressor, so any offensive moves will be by VN's alone and she definitely will pick on Taiwan's Taiping Island. Unless VN makes a lightning sneak attack Taiwan will the survivor of the two with superior air capabilities. But the big problem is while VN is in a sea struggle with Taiwan, China will position her naval arsenals nearby to pick off VN's remaining ships one by one and as well as her SCS possessions.
The other ASEAN nations will stay neutral because they know well enough China's not the aggressor, despite the forummer here make her to be, and willing to work with anyone that's involved and frankly they probably trust and depend on China much more than VN.
China is willing to solve the Huangyan dispute with PI peacefully otherwise she could've blown the PI warship out of the water a few months ago. What's her plans for the 40 shoals that VN occupies is anyone's guess. My take is she'll leave them as dispute area and let the future generations to deal with them so VN should be so lucky and keep her netizens quiet. One never knows what happen if he keeps stepping on the tiger's tail, so to speak.
Right, the US will not participate in war for disputed SCS. Instead, she will strengthen presence in the Western Pacific in general and SCS in particular, to ensure that all disputes in the region will be settled through diplomatic solutions. The most modern 4 high-speed warships go to Singapore, the increased presence in the Philippines, Thailand... well for that purpose.
Normally, the bully will pee his pants when he saw the US 7th Fleet.
VN will never attack the island which is being occupied illegally by Taiwan. Any attacking would also complicate the situation and break an opportunity to resolve disputes peacefully.
About China's claims, she claims "nine dotted lines" over 80% SCS, Even, it is located very very very close to the coast of Malaysia, Brunei, Philipines.
The "nine dotted lines" appeared first in 1948, it is absolutely ridiculous, unfounded, violating international law. Anyone with a clear conscience can easily recognize that.
About Paracels and the Spratlys, China had never controlled any island before WW2.
Taiwan occupied only some islands in the chaos of after WW2,
China only occupied illegally some of them after used force to rob islands from Vietnam in 1974 and 1988.
Therefore, China doesn't have any legitimate reason to claim the two archipelagos...