If sahil is the father ..then they would have showed that clearly..till now he did not say that from his mouth.All this is probably because of some other reason...may be Sahil knows the father..and as he knows that Mohini's pregnancy is because of an extra marital affair or an ilelgal contact..he is trying to save the family from this bad name. I hope this is true..i can't see Sahil in a negative character...he is the one who completely belong to Shantiniketan..born and brought up...supposed to be Bapuji's waris.