Rider Switch and FPP

I am putting together out TP and we plan to utilize Rider Switch quite a bit. Going with us is my husband, myself, our 4 year old who is 42.5" and our 9 month old. I have been reading that only one adult has to have a fastpass for that attraction. Is that right? Will they question why we both don’t have a fastpass? WE plan to use this also for my mom who is visiting Magic Kingdom one day with us. Since she has a single day ticket and isn’t staying onsite she won’t be able to book fastpass reservations at the same time as us. Any suggestions on how to handle that? WE are going to be at Magic Kingdom the 23rd and the 24th. Thank you!

We met 2 locals for one day at Epcot. I ended up scanning their tickets into MDE & then did fast passes for the group day of via the App. You won’t get your high priority FP’s that way, but it beats nothing. At MK, if you do that first thing in the day you’ll likely have some OK options (but not 7 Dwarfs). At Epcot it was somewhat limited…