We were a party of 7 (4 adults, a 7 yr old, a 4 yr old, and an infant) and I had high hopes of rider swap giving us some help but frankly it was such a pain point most of the time one of us adults volunteered to just skip the ride.
The short version of the issue is - if you all have FP, and the ride has a long posted standby time, the return window of the RS will come AFTER the time closes for the rest of the FPs.
Example: We all had FP for Soarin from 10:55-11:55. We showed up to do RS after our FP window opened (probably around 11 or 11:10). We went through the process of getting RS added, and the cast member even got my kids hyped to "ride twice". The problem? The return window for the rider swap was the current time + standby time, which when Soarin has a 75 minute posted wait time meant that it did not overlap the other FPs in the party. So, it was essentially useless unless our group as a whole wanted to hang out there for three ride cycles (one for the first FP group, one for the second FP group, and one for the RS people). We ended up not using the RS at all there - we just did the two FP groups.
We did use it successfully a handful of times at rope drop other places - after a situation at Test Track where we watched hundreds of people who were behind us at rope drop get in ahead of us while we waited for a cast member to figure out why his handheld machine that scans the RS to the bands wasn't working, we started putting the riders in the main standby line and made sure the rider swap cast member could see we were all still checking in/talking/together and then they could put the swap on the other riders in their own sweet time. But it was stressful at crowded places like Space Mountain...we kinda felt like jerks trying to make sure the cast member could see the rest of the party. And, the RS cast members are the FP cast members and also deal with the
DAS card folks, so they were often busy or there was a wait to get up there. At rope drop the standby times are short, so like Space for example, once the first set was done the second group was good to go since the ride time for the first group was longer than the posted standby, so the RS was pretty much immediately available when they got back, and we were done within a reasonable total timeframe.
Using RS with any sort of FP really didn't work for us. It really is designed for the first group to wait standby, and the second group to ride afterward using the swap. It just doesn't seem to play well with FP. In the cases where we already had FP for everyone, it never made any difference for us. No one ever managed to "ride twice" with the other FP people due to the time issue.
Maybe I am missing something too - I am sure I am no expert. But I really tried to get my head wrapped around it before we left, and it didn't work like I hoped.