Do all your adults want to ride FEA??? If not, I suggest:
Adult 1 takes tall and small child on Frozen (using their Tier 1 FP+)
Adult 2 rides Soarin' alone (using their Tier 1 FP+) and get a rider switch ticket for adult 1 and 3 and tall child
Adult 3 rides Test Track alone (using their Tier 1 FP+) and get a rider switch ticket for adult 1 and 2 and tall child
People may say this is manipulating the system, honestly if you have ever had to get two parties through the Soarin and Test Track lines it still takes plenty of time and it is allowed, not against the rules or cheating.
As for Rider Switch tickets having multiple days to use, also not manipulating the system, sometimes your youngest child cant wait for two parties to go through the attraction and you need to move on an come back to it later, and sometimes that later becomes later in the week. We had this on a very busy day in MK. I had taken our tall child on Splash with a FP+ and DH had taken him on Big Thunder, but it was hot and busy and it still took alot of time, little one started to lose it. We had to call it quits and head home for the day. We didn't get back to 3 days later to use those tickets so I could ride Big Thunder and DH Splash.