I I want to bring a 13 year old with me, I am 28, does that pass as him getting in without his actual parent?

Yes. You will just be responsible

You can sign the waiver online for the 13 year old. The 13 year old just has to be with an adult responsible for him/her.

You just have to do a waiver but you can do it online or when you get there

As long as he is accompanied by a adult its fine i believe they dis ask us to sign a waiver but never asked who was his mom etc