Living with family as an adult works better with clear agreements than with guesses.

Two adults in one house with different assumptions will collide, and the collisions get blamed on personality when the actual problem is that nothing was ever said. Guessing works fine until the night nobody guessed the same thing about the car, the kitchen, or what counts as late. Agreements are not cold. They are what lets everybody stop reading signals.

Pick the three things most likely to cause friction and settle them out loud: money, the car, and hours. Short and specific beats thorough. Then revisit it once after a month, because the first version of any arrangement is only a draft.