if that makes sense?
Yep. I was assuming you would need to build a timber frame within the opening as I couldn't see that in the last photo you posted (garages you're trying to buy). If that's not the case then you're all good opening-size-wise and can ignore me :)
Hadn't clocked those hinges either. They solve the "door in the way" issue.
If you ever forsee a situation where you're going from one garage to the other you'd have to go a bit further (minor inconvenience), but also would be quite isolated from one garage when you were in the other and might not see someone coming to swipe your bikes/tools/whatever (non-minor inconvenience), when with an up and over door you have a bit more visibility. This might be a non-issue based on location though, if it's not a through route?
EDIT: I'm a few pages too late. Just thinking of practicalities of actually having the doors, not how you'd build them. I'm not the person to advise on that!