Mother passed without a will

my mother passed away leaving behind a boyfriend she lived with, of 12 years, and two adult children. How do I go about getting access to her belongings? Everything she had is in the boyfriends house and he's going through everything of hers and deciding what stays and goes. With it being his house, I cant just walk in and take over. They were never married and Utah doesn't recognize common law marriage. There are things of my mothers, such as jewelry boxes and a photo of her parents, that I would like to have. Not to mention, I'd like the opportunity to look through her stuff see if I want anything else. How do I get access to my mothers stuff?