Relationship Stories for Family Members - Kids, and Toddlers,etc

I can't choose several of the relationships. I wanted sibling rivalry between the brother & sister in my family but after the initiation event, sibling rivalry wasn't an option. I also wanted to start a frenemies relationship between the son & another male sim that looks exactly like him but that wasn't an available option after initiating a relationship either. Are relationships only available after reaching a certain level? I'm on level 24.