Is it illegal for non-executors to take a deceased person's property from their estate to keep or sell? Even if they are related (niece).

My uncle died, his legal partner (California Marriage) committed suicide. Partner's ex-wife took stuff from the house. Uncle's niece then went and took the rest of the stuff for herself. An executor has not been established, but she did find both deceased parties' wills. She is posting pictures of her "loot" on facebook and bragging about what she is bringing home.