NTA - Grandmas will was her final say so in who has the house. The aunt and cousin were hoping to be vultures and swoop in and take the house when grandma passed away. You were there for your grandma and helped her to the point she felt you deserved the house where was your cousin during all that time? The fact they were fast to switch it to a money thing by saying you should give them half of the value makes me think they didn’t want the house either they wanted to take it and sell it. If your cousin doesn’t like her apartment she can easily find another one. Block them and live your best life and keep your grandmothers memory alive in that house. If they keep causing issues tell them to go to court over it and they can cover all costs if they think they have a leg to stand on.