As per police my father has full right on the property because he is her husband and if he has given the permission to tenant then she has to accept it and cannot ask them to leave.
The statement of police is incorrect, They are ignorant of law.
They do not have power to interfere in civil matter. This statement by police is out of their sheer ignorance of law. Since the property belongs to your mother, she has full rights over it, your father cannot lease out the same on rent, your mother can approach court for eviction since the tenant is having a legally valid agreement no doubt executed by an unauthorized person.
Somebody says file tresspass section Section 441 of Indian Penal Code,
Trespass law will not be maintainable since the tenant is having a valid rental agreement.
somebody says file an eviction suite in court & it will take 7 years
An eviction suit will not 7 years, it can be disposed within two years also. But this shall be the only remedy to remove the arrogant tenant from the site.
somebody says my father has full right on property.
Incorrect. Your father ha no rights even for handful of mud from the property. Your mother shall be absolute owner as per law.