Hi
Since Party S has entered into an MOU with you and that there is also a No Objection certificate issued (ideally from Party S to Builder), there is no requirement for presence of Party S at the time of builder registering the property in your name.
So the steps should be as follows:
1) MOU between Party S and you.
2) No Objection certificate from Builder and Party S for registration of property in your name.
3) Assignment deed between Builder and Party S in which party S will assign his rights in building and construction agreement to you.
4) The builder can register the property directly to you with out Party S .
5) Party S or his descendants cannot claim that the transaction was done under duress or coercion as
a) Party S is in China and out of physical reach of both you and buyer.
b) Party S is signing multiple documents that is (the MOU, No objection certificate and assignment deed).
c) Since you will be paying Party S through your bank 90% of the sale value, your transaction is legal in accordance to law.
6) Another alternative to the whole of the solution which is totally secure and eliminates any warranted future risks is
a) Party S can execute a special power of attorney document in your favour in Indian embassy.
b) MOU entered in to between Party S and YOU with both party 2 and you as signatories.
c) No Objection certificate from Builder and Party S for registration of property in your name.
d) Assignment deed between Builder and Party S in which party S will assign his rights in building and construction agreement to you.
e) Registered sale deed between Builder and You with Party S as a consenting party and the signatories in this sale deed are builder, you and Party S represented by power of attorney holder(you).
Hope this information is useful.