So if you state in the written agreement that tenant is to pay all utilities to include but not limited to, blah, blah, blah, and if all adult parties sign, you have a legal contract.

If you do not want to rent to 4-5 adults (each on the lease, 4-5 credit checks) there is nothing that requires you do in most markets.

Depending on local laws, send renewal notices in advance of the end dates, specifying a requirement for an in-person meeting with all adult occupants by a certain date; provide them your application form to be completed and returned to you prior to this meeting so you can approve them; and advise them of the terms you will offer if they are approved.

I treat my tenants as adults.  

Two 21 year old females decided to rent an apartment, it was easy to qualify since one of the tenant's mother works as the property manager for the owner who is also active in management.

I'm not that much older, and have very strong FICO Scores (760's) but.. from my research, haven't really seen banks excited to lend to young adults.

Sometimes the adult kids stash their parents there.

Because families tend to rent big units so it makes them less risky compared to single adults that may ruin and not take good care of their living space2.

My thinking is that four adults will cost a lot more in utilities, but I’m not sure if raising rent is something commonly practiced when there are extra tenants.

He was 18 (adult) and got his 15 year old girlfriend pregnant.