Emily really is in an impossible position. She could either be honest about being angry, which would make Ross unhappy, or she could pretend to be cool with it, which would not address the problem at all. And oh yeah, Ross said someone else's name at their wedding. That's sitcom hijinks twisted into pure horror. Would you be OK in that scenario? I know that chillness is a virtue, but it's fine to have some self-respect! "Wait ... am I the 'bad choice' in a love triangle? This isn't going to end well for me, is it?"
And Rachel is an active threat to their relationship. She shows up at the wedding with the exact purpose of breaking Ross and Emily up. She feels encouraged to pursue him when things start to fall apart, and even decides to tell Ross that she loves him after she sees all the crap the couple has gone through. Maybe it wasn't her intent to make the situation worse, but none of that really improves Ross and Emily's failing marriage. But then again, this is Ross, the same guy who later tells Rachel to abandon her dream job to be in a toxic relationship with him again, so maybe the whole thing was always gonna be hopeless.