Property of grandmother occupied by one of my uncle

After grandmothers death, her apartment is disputed. She had three sons. My father,the eldest. Second died and third is in US. He returned to perform the rituals with us.It was decided that the apartment will be divided into two parts between my dad and him as dead uncles family does not want a share.Within a week he sold the furniture present in the house and took the money. Now the youngest son has changed the lock moreover he has given the power of attorney to his brother in law without informing my dad.There is no will. What should be our next course of action? We are Hindu