Yes, now mother can make will of her share, not of whole property because he is no more.
In father's selfowned property belongs to everyone now, means all children are legal heirs in the property.
Now you tell me still your mother want to make a WILL and registered with sub registrar as a between tester and beneficiary , a third person most of the time lawyer is the executor and 2 witnesses.
Property papers, stamp duty and registration fees, both the party, lawyer, witnesses, registered in sub registrar office.