well, right now I feel it is Soham who is the son of Balbir but there are 2 possibilities:
1) Manpreet wanted to help Rano in some way or the other.. so, she might have brought Rano's son(Parmeet) into her house as her own son while she gave her own son(Soham) away to buaji who might be a close relative of Manpreet.
or
2) Rano gave her son(Soham) to buaji or Angad's mother.. and buaji must be knowing about this.
I think the second one is more of a possibility!