Not sure how this would work out. I can see an assistant coach working with a senior coach for high-level competitions (e.g., John Nicks is 86 and coaches Ashley Wagner with the help of an assistant coach; in particular, John Nicks doesn't travel with her to competitions). And I know some skaters at my rink who have one coach for freestyle and a different coach for dance. Different coaches for different skills. OK.
But if you have more than one coach working on the same set of skills, there can be the problem of inconsistency. There is usually more than one method to teach a skill, and each coach has her pet techniques. So if Coach 1 teaches particular arm and leg positions, for example, and Coach 2 teaches different arm and leg positions, you'll end up with one very confused student. There's also the question of continuity. For example, when my coach introduces me to a new skill (e.g., consecutive back outside edges), she'll first show me the proper way of doing it. I'll try it, and if I make good progress, I'll continue as such. But if I try it, and continue to flop, she'll have me back off (e.g., change my arm and leg positions from the proper ones) until I acquire better balance and confidence, and then have me do it the proper way. Similarly, if I'm doing a sequence (e.g., a waltz eight), and she notices particular weaknesses (e.g., my RFO 3-turn), she'll have me do remedial exercises before continuing. But if you flip-flop between independent coaches, there's no way to keep track of what's going on.
If it's a choice between Coach 1 ("best" coach, but not readily available) and Coach 2 (maybe not quite as good as Coach 2, but competent and readily available), I would simply go with Coach 2; a sporadic mix of Coach 1 and Coach 2 (contingent on the availability of Coach 1) might actually slow progress.