I just wanted to follow up with my results.
First, I noticed that I was going to get charged a $25 booking fee for each reservation online, so I decided to go ahead and call and book them together to save $25 (or so I thought). After about 20 minutes on the phone giving all info (the reason I wanted to do it online) for the first room, they were going to charge me $25 and then go through it all again for the second room and charge me again. So I thanked her for her time and said I would just do it online if I had to pay that booking fee twice either way.
In less than 5 minutes, I had both rooms booked online. Nowhere did it ask for our Royal #'s. Then I log into my Royal account online & it had my reservation there already (assuming it matched name & birthdate). Then I searched and found my kids' reservation on my computer. Right after that, I opened my app on my phone and it had both reservations there. Much easier than I expected.