After neil-ragini got separated with legal notice of their children custody , ragini at that time was expecting , she didnt told neil because she thought he would take away this kid from her aswell. When she was delivering the baby pam was present their for some reason she saw the baby and took it away as its her brothers child ,bribing the nurse to tell ragini that her kid died while she gives birth.
And ragini doesnt know about suhani as her daugters existence . While pam took suhani to neil telling him that ragini hided her pregnancy and dont want the kid with her or told neil that she hided the pregnancy as she wanted to keep the kid away (thats why neil and pam told agam and suhani that unki maa was a manipulative women) and neil says (na wo achi maa bansaki)
Thats why ragini doensnt talk about the kid and neil doesnt talk as he thinks (jab ragini ko suhani chai hi ni thi toh baat karny ka faida) or he feels hurt that how come a mother cant ask about the kid.
Because if suhani was adopted so why to hide her from ragini why would she bother, or adopted hoti toh neil could just ask ragini to hide the fact as he asked her to stay away from kids . Or if she is pam's daughter why to hide from suhani? She could be happy knowing .
She sent suhani away as agar wo yahan hoti toh yeh raaz khul sakta tha and if that happened suhani would be hurt knowing kay usky dad ny uski mom say chupai baat. And if ragini finds out she wouldnt let suhanj go and neil wouldnt let suhani stay so he will have to stay too.
So i think suhani will be the reason of both neil and ragini uniting . Suhani is the main kid.
But hopefully she is their girl only. As she is innocent and beautiful like purani wali ragini and intelligent like neil.