You are married to a man that has grown children from a previous marriage and he dies do they have any rights to property?

If the man died intestate in any state, the state has rules for dividing his property after debts are paid ( the first purpose of the probate law is to pay debts, then you got an estate to divide) each state is slightly diffierent, but generally, the living spouse is entitled to a certain interest, or division of his property after debts are paid, and then his children or their heirs.

Next, frequently forgotten when people with spouses die and die intestate, is the spousal 'years support' provission which provides for special treatment for one year for the widow or widower.

Each state is diffiernet...each state is diffierent.

and if he had a will, it depends on what he wrote on his will.