You can unlock the campaigns in any order, and the level requirement for unlocking missions is based on how many campaigns you unlock, not the order which they're unlocked. For example, if you unlock Council Apocalypse first and your friend unlocks Hades Betrayal first, you'd both require level 21 for the final mission of the campaign you chose to unlock to be available.
If you're playing with friends, you have access to everything that's available to both of you, meaning that if they unlock a campaign you haven't yet, then you can play it while you're in a group. That's why your progress looks so different.