Number 3s are actually the worst ones because those are mostly ones with bosses with more than a few health gauges so in addition to Jack you probably need a couple of other guilted attribute-specific medals as well + a tier 2 STR buffer. If you can't do #3s, you might still be able to do many of the #4s (since enemies in those are high level but often only have, like, 3 health gauges), Jack Skellington completely obliterates everything & anything in those, you just mostly need some medal with APP so that you don't run out of Jack's special nukes. So just make a choice who to give APP to (if you have any half-decent AOE medals with a cost of 1, that's your medal) and try #4s if #3s are still giving you trouble. I mean, I did most of my #4s with basically nothing else but
Piglet w/DBII
RAX w/APP (this could probably be any medal with APP since in most missions this didn't do all that much damage, it just gave me the occasional special gauge refresh)
Jack Skellington 100% w/ABII Max
Jack alone didn't necessarily one-shot everything, but it left most of them with so little health that just using normal attacks with the rest of the medals was usually enough to kill them, with occasionally using either the 100% guilted 1000/1000 Chipped ABII BC Mickey (that you also now have access to since you joined our party) to clean up what was left if they still had ~1-1,5 bars of health left or if that felt too draining, used one of my own better (cheap gauge cost) medals or one of the other good friend medals in our party (Illustrated Terra has APP and is pretty strong as well, which is very useful).
The rest of the medals weren't needed most of the time. I pretty much never used their special attacks to save special gauge and was still able to beat the missions.
If you need it, I can share my (IIRC) 100% guilted Musketeer Goofy, which should prove helpful at least in missions with green enemies. If you need something specific that you don't see being available, you can try to ask it in the party chat. If we have something helpful, we'll happily share.
EDIT: And you don't need +25. I didn't have one for most of the Adamantine quests.