That's all I know. If anyone knows anything about the last two, help would be greatly appreciated.
Considering the devs specifically stated there's going to be a Medic-focused challenge where you have to keep your team alive, and it's all about deciding who to heal/revive and when, I'd say Tower Defense will be a mission where you're a medic and have to defend everyone while you're in a tower.
Assuming the Escort Duty level is an Engineer-specific one, that is.
Either way, ONE of them IS a medic challenge.