If I have my child's friends coming with us is there a hard copy waiver to have their parents fill out?

Yes they also have a kiosk to fill out waivers when you arrive

Yes, just do it online before you go and you should be good.

Yes you can also fill it out online before you go to save yourself some time. The parent of the other child can do that as well. Just have the child's name and birthdate so they can verify the waiver was done.