Inside any polyship there are mini relationships inside that require TLC. It's the polymath thing.
So you see there is a problem on the "Sarah and Mike tier" of this... emerging baby polyship trying to take flight (?). (Sorry... I am not clear on what it is. That is part of all this problem!)
Does JOHN see that there is a problem on that "Sarah and Mike" tier? If so, and you both claim to love these people (as friends/lovers/romantic partners)... could you give them the space/time needed to sort themselves out? Could you guys step up to say something like...
"Look -- we see a problem in this tier. Until that is resolved and you guys are solid in your own relationship tier of "Sarah and Mike" -- this polyship cannot fly straight. Mike is unwilling to state his wants/needs for things to stop. But clearly Mike is unhappy. So let's stop. Give space/time required so things can fly right. And if it isn't meant to be, it isn't me]ant to be. But let's not throw Mike under the bus. It is not kind. Mike -- what kind of support/help do you need right now? How can we be good friends to you and support you in appropriate ways?"
I don't think all your players agreed to the same kind of open relationship model.
Are you all on the same page for what it is you have here?
It's like everyone went in assuming it was whatever it was (in the mind of the person thinking it). But Mike seems to want it to be like swinging -- play partners and friends. The rest sound like they want polyamory? But maybe you seem to want a primary-secondary model?
I'm not sure what John and Sarah want. Does John want a co-primary model?
Maybe you could talk in quad and sort that out? What IS this 'ship you are trying to fly here? What are everyone's wants, needs, and limits? How often are you going to check in to make sure everyone's needs are being met?
Don't all players deserve to feel safe in polyship? Mentally safe, emotionally safe, physically safe, spiritually safe? If so, how can THIS polyship make it so?