Hi everyone! We're back from four days in the park and we used MaxPass for three of those days and rider swap as well. RS worked quite well for us. I purchased MaxPass for one adult and my older child, and used RS for the second adult, and of course my youngest didn't need MaxPass. It was a bonus that we only needed to purchase MaxPass for 2/4 of our group. For the fastpass rides that my youngest could go on, we just pulled paper fastpasses (Toy Story, Haunted Mansion, Buzz).
As for return times with RS, we almost always were able to switch immediately. I was using the app on my phone, which will show you the RS "fastpass" when the CM loads it onto the "swappers" tickets. There is a return time attached to it, but it was usually for 10-20 minutes later (and good for one hour).
The entire group does need to be present, so the CM loading the RS passes onto the tickets can see that you have a little one who can't ride. This didn't necessarily mean waiting in line (hard to do with a stroller), but just hanging nearby (to the side of the fastpass return line) and the CMs at the first scan station.
There was one instance on Splash where after my daughter and I rode, there was still a 20-30 minute wait until the swap passes started. We had already waited an hour for our fastpass window to open.. so we simply asked the CM if we had to wait around for another 30 minutes (explaining that we just wanted to swap adults), and he said no and let the our second group go through right then.
It seems that CMs are definitely "guesstimating" the rider swap return window, so it's not a perfect science, but as I've said, it almost always worked out that we could swap immediately, which worked well for us.
This was my son's first visit and our first time using RS. It was nice that there's usually a ride close by that he can go on while group 1 is on the "big ride" (Winnie the Pooh, Jungle Cruise, Buzz, Maters and Luigis, Bugs Land right next to GotG and Monsters Inc, etc).