That is a great question. Since the room isn't very deep (front to back), it doesn't allow for a lot of separation between surround speakers and the overheads.
One thing to consider is that you have 5 seating positions that are sideways. Those will be compromised in all sorts of ways if used for movie watching. I would cater the sound more to the main 6 person seating in the back. That is where a bulk of the movie watching will happen. In fact, I would be tempted not to worry about the sound for those seats at all. If you end up having a lot of people over to watch a movie, and you turn those other seats towards the screen, they will have to be far off to the sides so that they aren't in the way of the main 6 person seating, so no sound field is going to do well for those areas.
So if you go 5.1.4, then you should move your side surrounds further away from the screen, and bring your in-ceiling speakers closest to the screen back as well.
If you go 7.1.2, then the surround placement is OK. I would rather see the side surrounds closer to the main seating side of the room, especially since it would put the 2 in-ceiling speakers in front of the listening area anyway.
Here are some initial rough ideas about a 5.1.4 and 7.1.2 layout for your space with focus on always playing things back in either Atmos, DTS:X, or one of their upmixers. These layouts will provide room filling sound, good separation for Atmos/DTS:X overhead speakers, and still be closer to regular standards. I tried to keep your limitations/compromises in mind, but may have moved something to a location that would be a placement issue physically for you too. Only you will know that. I also did NOT touch the subwoofer placements.
I apologize for their crude look. I just did copy/paste/erase of things that you had vs. recreating the speakers that you have drawn up.
