Yes, technically those are the only coasters that flip. As a warning, the Rip Ride Rocket doesn't technically go upside down but it nearly does a few times. The big loop is outside and right by the entrance so you can see what it looks like.
Harry Potter and the Forbidden Journey isn't a coaster and doesn't technically twist you into a loop, but there is one part of the ride where they dip you backwards, to a point where your knees are higher than your head. It's a little hard to describe but thing of being on a dentist's chair where they pull the chair up and lean you back a bit. It's really only for a second and most people don't seem to even really notice it, because there is just a lot going on in the attraction. Personally I too hate roller coasters that flip or loop but I can do Forbidden Journey over and over.
And yes, there is always a place you can stand if you don't want to go on the ride, basically a "chicken exit." Just ask right before you get into the ride vehicle, or when the attraction attendant asks how many are in your party. For some rides (Forbidden Journey for example) you basically just step a little to the side and will see where the people get off. For some other attractions you may need to walk through a hallway or around the corner. Either way an employee will direct the person to where they can wait and where the ride exits. My one warning is that an employee may not allow a 13 year old to stand alone without another adult. You may want to check with the employees at the front of the attraction just so there is no confusion when you are about to board. However, I remember going to Universal on a school trip when I was 14 and waiting alone for some of my friends to go on a ride I didn't want to, so I think you should be fine.
If you do split up, it might be smart to have a set meet-up place just in case, especially if you had to store a cell phone in a locker. For example, it might be worth going into the "dump" exit gift shops before the attraction and picking a specific location to meet at (ex. by the Spider-Man mug display at Spider-Man). This is from personal experience recently as an adult - a friend and I went on Forbidden Journey as single riders and planned to meet up at the exit. Even though my friend was seated in a vehicle behind me we somehow just missed each other exiting. We did find each other a few minutes later, but having a planned spot might not be a bad idea!
