See,dadaji has two sons and a daughter.....Her two songs are alok(rano's husband) and the other is badi ma's husband...Now dadaji also have a daughter too but she is not alive.She was the only daughter of Dadaji........This dead daughter's son is Elesh............Actually for Elesh this is his maternal grandfather's house.......so he is Ishaan's cousin brother.. : )
Hope u understood.Really a bit complicated relationship
Radha doesn't have any blood relationship with the kashyaps.....She is an orphan who has been living in the kashyap household since she was 14......Maybe dadaji adopted her or something.. : )