So you have a few Snarky Partners (sounds like a podcast dedicated to Shit talking Starbucks)... I say tell them to either hook up or hash it out.

create boundaries. tell them they can disagree in the back and not to have it interfere with your work on the floor. otherwise, speak with your manager/refuse to work with them together.

You are not getting paid to be a barista AND a counselor/mediator. It’s your manager’s job to manage interpersonal issues with store staff. they are paid money to take care of this. Obviously, you should still be a normal human being with feelings, but don’t let the responsibility fall on you to fix it. Do what you can and push back when you have to. And pressure your manager to take care of it. Set your boundaries and let them know what you’ll tolerate and what you won’t. The sad things is sometimes you have to step on toes and make enemies when you’d rather not. I get it. I just want everyone to like me and get along. But I’m already working way too hard to also fix everyone else’s interpersonal drama. If they can’t keep their toxicity to themselves then I have to put up some walls and let them stop being my friend.

You need to talk to your SM and explain how when they work together it’s disruptive and counterproductive.