It says 21 to rent a handgun. I am 18, but if my parent is with me can we rent a handgun? Also same question but if we were to include a 16 year old as well (as a group of 3)? Or would we need to rent a rifle?

If you are with your parents they will be renting the firearms. The 16 year old may shoot with proper parental supervision.

It wouldn't be "you" renting the gun. It'd be the "trainer" in that case. If it says to enter/shoot then you can't participate.

Call them they will be happy to answer your question

Call the gun shop, why would you ask a serious question over the internet?