Acknowledge that it’s risky business, don’t expect people to thank you for keeping their relationships. Understand that walking away will always produce better results for you personally than actually staying and trying to untangle this mess

Grab their attention, ring a smoke alarm, drop something loud, slam the door etc

Separate them physically and give the time to cool off

Convince both of them that family therapy is normal, beneficial and overall “worth it” regardless of how bad the things are