My father died reasonly left no will.he had 6 children,which wife and a brother are deceased.so who will be intitle to his estate?

It passes equally to the next of kin.

Where did your dad live?

One cannot answer that question with any precision with out knowing which state or country he died in.

Generally, the "intestacy" (which means "no will") statute in your jurisdiction will control who inherits. I would expect that his children would inherit most or all of his estate. And it is probable that someone will have to apply to the court to "probate" his estate. It's not automatic.