@Becky201068 As you've probably seen from this thread RotR can be a bit confusing. As you have eight kids, hopefully the advice in this thread can help. One thing I highly recommend (based on reading and so you don't have to go back so many pages), next week the park opens at 7 a.m. Try and be there before 7 (preferably it seems between 6/6:30 very latest) as you will need to be IN the park in order to get one of these boarding groups. Make sure you have My Disney Experience app on your phone and make sure it's working properly.
When you open the app, you'll notice the Rise of the Resistance likely right when it loads and a "Find Out More" button. Then you'll see "My Status" and "Join Boarding Group," latter of which will be greyed out right now. At opening of the park (7), as I understand it that Join Boarding will go red, (if it doesn't, it sounds like either exit out of the app and come back, or the back arrow at the top left of your phone and then click Find Out More again). Click Join Boarding and it will give you a boarding group number. The app will tell you when your boarding group is called (be sure to have Notifications turned on for the app) and you have two hours to return to the ride. Please note, the ride has been very popular and sometimes the boarding groups have filled up by half an hour after park opening (though it could change next week as crowds get a bit smaller), hence be there early.
I'll let others though refine this a bit if I'm missing something