Today, write something about one of your siblings. If you don’t have a sibling, perhaps write about how you feel about that, or about a person who is like a sibling to you. However this lands for you today, write about that.
Alternatively, you could also approach this way: write your sibling’s name (or the name of your stand-in) in the center of a piece of paper, and spend some time brainstorming all the possible ideas of things you can write using that. For example, my sibling is a scientist, so I could write about: my relationship with my sibling, the work he does, his field of study, the town he lives in, and so on.