Rules state Squads may have up to "2" Guests.
Ammo 6 or less and up to 15 is a huge range!
Your squad has posted 4-6 pilots. For planning we "really" need some consistent numbers. I know it is rough since I run a squad also, but to be fair to all involved you need "some" reasonable commitment. Maybe if you have four guys that can only make it ½ the time they could trade off. That way you can count 2 every Friday between the 4 of them.
Fuel 1.5 which will give you approximately 30% more range.