My brother lived with my father for several years just before and well after he retired. I lived with them for several months when I was 45, and another brother lived with them a year or so before I did. Dad had a big house and a rule: He would not help us out financially, except with a loan for which we paid bank-level interest, or by letting us live with him while in transition or going to school. Both brothers were attending school when they moved in. I was transitioning from another state.
We shared duties and minor expenses. We helped with food, keeping the house clean, and maintaining the yard, but didn't have to pay rent. The others had their own transportation. I shared Dad's car until I moved out.
Dad was not married, so there was no problem with a spouse. He very much liked the company. We were family. We were an attraction for the rest of the family, so we had big family gatherings there at Thanksgiving or Christmas.
Dad was very lonely when we moved away. He soon sold the house and moved closer to where my sister lived, then closer. Still lonely, after a few years he contracted an infection and passed away.