Walikum Assalam. If you are forced to leave a place where you can not live like a Muslim and people in the former place trying to kill you, then you have to leave the place. And if your family are not ready to follow you, you have to leave them behind too. I think the same thing happened with Prophet Ibrahim (Alahi was Salam). Allah knows the best.

We know that a lot of Sahaba's [Companion of Prophet (PUBH)] relatives (father /mothers) didn't accept Islam at first. Sahaba (Ra) didn't sever the bond from their side (exception may be there, I don't know of) and kept trying to convert their relatives to Islam. But, on the other hand, Who didn't accept, rather came to fight, were even killed by Sahaba's (Ra)! My point is "don't sever the tie from your side and keep trying to convince them". If they sever the ties, Allah is the best protector.