This is still confusing me and now I’m not sure what to expect in our situation. I booked FP at the big scary rides for my husband and friend and booked a kid friendly ride for myself, son (who is too little) and sister. Would my sister and I be eligible to get the Riderswap for the big scary ride based on the standby time at least?
From what we experienced, no this would not work. I have one child who won't ride anything "scary" so my younger daughter gets to double up on her FP for ToT and other things. We are a party of 6, and I split FP like you are doing to accomodate every one. Last time I tried to get a rider swap for ToT with only having 2 FP (myself and my daughter). Since no one else had FP for it, we were not eligible for rider swaps because there was no other band/ticket to attach the rider swap to.
I have no experience with stand by line and rider swaps. We only tried it with our FP.
Potentially, you could make FP for scary ride for husband, friend and sister. Sister sits out as the rider swap band/ticket. Then you, sister, and one other could ride scary ride together. You and kiddo could FP something else while waiting for others to be done with scary ride (the first time). I *think* this is how it works. But I'm still trying to figure it out. It got to be that we just used the big scary ride rider swap time as bathroom/drink/snack break time rather than trying to accomplish something else.