Well it's a simple majority thing. Whenever a vote kick comes up, it's the 3 players who aren't being vote kicked that have the votes. That's 3 votes. If there's a couple, they have 2/3rds of the votes. It's always been this way.

And yeah, couples in my experience are pretty assholey about kicking, because they know they can do it. I even have a couple of friends who kick people pretty much every other time they run dungeons together, because they can't stand people at all who give them a hard time or consistently play poorly. I myself have run into myriad couples who do shitty things in dungeons, that aren't always outright kicks. And of course it goes the other way sometimes, where you initiate kick on one part of the couple. As long as the other person votes yes, it usually results in both partners in the couple leaving.

I have no idea how they'd implement it, but it would be kind of nice if they could make pre-made portions of dungeon groups count as a singular vote. That way it would be 2 votes or 1 vote, and couples wouldn't be able to flex a power they really shouldn't have.