Never appoint two people to lead something, instead…

Always make one person the leader. Always make it clear that, in the case of a disagreement, one of them gets to make the call; one of them bears the responsibility.
If you don’t appoint a clear “leader” the two (or more) leaders will have to come to a consensus on every single issue… And that’s fine for most things, but sometimes you just need to make a call and run with it, rather than spend hours, days, months trying to make the other person happy.
So, appoint two leaders, but always then say, “if you can’t decide on something, I want Person A to make the call, ok?”