2. He cannot be son of Vaishali because always she said "Mere 'Do' betain" in many dialolues
3. He can not be son of Susheel, as Susheel did not show any emotion of recognition (May be he knew, Vikram would be coming)
He could be one among Purohit asset contender. He could be Dev's cousin or Dev's friend. This Vikram can not be a third contender separate from Susheel because he would be the first one to drive him away.
I think Vaishali will stop acting bad Mother In Law once she realizes Vishaka is married to Vikram and may start accepting Radhika. But there is always a chance that she would start looking at "Fourth" Choti Bahu 😉