I think you should define tiers man, this is too open-ended, right now people can have weaker characters at higher levels but no higher levels at lower ones like Zoro as YC3. Another thing is you did not mention what pirate age are we restricted to, e.g. we can have Oden (who was a commander but is Yonko level) or even pick anyone from Rocks except Rocks (since he was the captain and the rest can be commanders). What about Aokiji (he is allied with BB) so can he be my YC3?
Considering we cant have declared Yonkos and Admirals as part of our crew then I would have:
If we can only have the current ones and no YC can take another's place in the ranking then:
2. Lucky Roo
Zoro is a Yonko himself but I get it since he is under Luffy command.
Doflamingo is nowhere near YC2 level.
Hancock is another Yonko herself.
Enel is nowhere near YC4 level. At least what we saw from him pre-timeskip.
Yonko Ally: Luffy(plot armor won't let me lose)
YC1: Zoro(pure strength won't let me lose)
YC2: Cracker (without plot armor from Luffy he is undefeated)
YC3: Shiki (because I guess he was YC3 of Rocks)
YC4: Yamato (because if Kaido had any YC4 could only be her, not that she is weak but it is clear the position of others)