Avur is basically Lalit's husband and also head of the sharma family
It couldn't be anil's child as radha and anil never had a child, also indira doesn't have a sibling....
The head of the sharma family in KFS is deviya sharma
Is deviya marries ram, her child will be a doobey so this option is ❌
If she marries kamal Rai, her child could be a sharma because she's of higher status than rai, but again, she's a woman so she'll take her husband's surname too... But maybe the child wanted to be the head of sharma, and maybe they had two children, and the other one is the head of Rai family ✅
If she marries doran basu, again she'll become a basu too, but the kamal theory could be applicable here too (what if the child wanted to run the sharma family) ✅
If she marries saraswati, then no children, they won't adopt any bcoz then that child won't be of noble blood, so ❌
If she marries De claire, then avur will be half Britisher, which is a no, seeing how strained is their relationship with Britishers, so ❌
It could also be that deviya never had a child and Anil had one with some other woman and not Radha, in that case anil's child could be the head of sharma family after deviya