It's not a case where young adults were living with mommy and daddy until graduating and now wanting to rent their place, or someone who owned house until they moved to a new city, want to rent because they are so new. 

You can kick them out, but I prefer to try to create situations that are not likely to develop into problems and holding everyone equally responsibly goes a long way in the right direction.In your case it sounds like you have college students or adults at an equivalent or lower level of responsibility which is very common renting out at the room level. 

If the applicant is interested, I supply either a printed copy of the application for each adult to fill out or I offer to email the person the application to fill out. 

I have lived in the city my entire adult life and own, now, 4 investment properties in urban Indy.

Along comes a grown adult who wants it, HOORAY! 

You need to get over them once and become an adult.

I have no problem if an adult books for their kids.

With a puppy as opposed to an adult dog, however, you can basically guarantee there's going to be damage, so I would consider that in whatever you're going to decide. 

I also take this time to inform all Tenants their Rental Agreements WILL be non-renewed at the earliest lawful date, and IF they wish to remain, they will need to complete a new Application, providing the usual supporting documentation, and if approved, all adults will need to sign a new Rental Agreement with your terms and conditions.

Usually, if a cellar has any windows, the windows are too small for an adult to fit through.