1. The caption of your query is "My husband has owned a property on lease from his grandmother". Please note that title of a property can not be owned or a property can not be owned by virtue of a lease deed but through conveyance deed or will.
2. What your husband had was lease right or right to stay and/or use the property as per the terms mentioned in the lease deed.
3. Whether the lease right will be transferred to his legal heirs after his demise or will be extinguished shall have to be mentioned in the said lease deed.
4. If the lease right is transferable as per the lease deed to his legal heirs, then get a relinquishment deed registered by your son duly relinquishing his share on the lease right in your favour.
5. If his mother is no more and if the lease right is not transferable, then the title of the said property will be equally shared by all the legal heirs of your mother in law including your husband ( i.e. you and your son after his demise).