Must a person declare a primary residence?

I live with my girlfriend, but my older brother has provided a place for me to conduct commerce and allow my 20 year old son to live and my other two 21 and 14 year old daughters to visit. I am 50-50 at these locations. Can I legally do this? I would like to use the cardiac facilities at the hospital which I attend where I've lived for over 6 years. But I would like my 14 year old daughter to move into the house my older brother provided, so she can go to the local high school there. Both locations are about 20 minutes away from each other. My son, attends junior college now at the local college, and he lists the residence that my brother offers.