What was the method by which your grandfather transferred property to the name of your mother? Was it registered?
Your mother has complete rights over the property even though father constructed house. All children have equal rights but while she is still alive, she can transfer it.
For further queries, you can contact me at firstname.lastname@example.org
This is Matter of partition and separate possession as per law
How the property transferred to the mother please clear it then I can answer your question
You can call me for advise
Advocate Shaikh IRFAN