My husband passed away he is holding bank fixed deposits in private bank and has made me nominee in the same ,however the bank refuses to give me the poceeds and asks for signature of all legal heirs --can they do that ? And what shoulld I do my children stay abroad what should I do ?

It depends on how the accounts are titled. Making you a "nominee" may have ended with his death. So they may be within their rights.

Have you submitted his estate for probate? Did he leave a will?