Adiyen had done Samashrayanam; after listening to many upanyasams, adiyen desires to do Prapatti. But the elders at home worship other gods along with Perumal and celebrate their festivals too. In this situation can adiyen undergo Prapatti and what are the post prapatti requirements?

When the elders of your family worship and celebrate other gods, you can remain detached from it. We are not against other gods. Since we are devotees of Perumal there is no need to worship other demi-gods.
After performing prapatti one must not worship other gods and partake their prasadam.
It is written in saiva agama that one must not accept the prasadam of demi-gods but now it is been altered by their followers. The learned Vaidikas will not accept those prasadam. We are not stating anything new here. They will rectify this fault in future. So, without feeling guilty one can continue to contemplate on Perumal alone.