How do I divide rent and utilities?

[Wojciech Grajewski]

I am finishing a total interior home renovation on my home. The house is 3 bedroom, 1.5 bathroom, full unfinished basement, one car garage, and the home is located in Long Island, NY. Currently my cousin is living there (he moved in 1 Mar 2019. We have an agreement that as long as he is finishing up the renovation on the home he can live there for free. My cousin should be done with the renovation 1 july 2019. At that point I would like for him to start paying rent. He was paying $500 to my aunt when he was renting a room in her mobile home. So I could charge that much if I wanted since I know he can afford it. The second issue is I would like to move in my parents to my home at the same time. I know my parents are paying $1,400 a month in rent which includes gas, heating, electric, and water. They pay for Internet and cable on their own. The problem is that they are in their mid sixties and cannot afford to live on their own. I was thinking charging them $700 in rent and have them pay the utilities on my home out of their own pocket. The question is: If my cousin is living there and using minimum utilities how do I divided the utilities once my parents move in? In short I could collect from my parents $700 and my cousin only $300 (not the $500 i know i could since I want to help him out). Just want to have everything fair. Any thoughts on how I can make everything fair? How would you handle this situation? Thank you for the input.