Agricultural land

Presuming you are a Hindu by religion, your son will fall under class I category of his father and entitled for a legitimate share out of his deceased father's property as a right.

According to your profile, you are a Hindu; therefore, your son will inherit his share of his father's property.

According to hind law your Son only legal heir of deaced father 

What about the mother of the deceased? Is the son the only child?

Deceased (father) son is entitled to get the property.

Yes son is the only child. 

If your father in law is refusing to give the property that was on the name of your ex husband then you can file a permanent injunction suit against your father in law from preventing you to take possession of the property on behalf of your minor child and restrain him from  interfering with the property affairs subsequently also.  You can get the revenue records transferred to your son's name from the revenue department by producing the legal heirship certificate and the death certificate of your ex husband and your identity card to prove that you are the nuatural guardian to your minor child

Your child and his/her grandmother are class I heir of your ex if you are a Hindu.

At this stage question of payment for alimony or maintenance cannot have any effect in the property left behind by your ex .

Thank you sir. I have just given a context of what has happened in past because father in law troubling us a lot.