Finding the best place for those rear speakers can be a bit of a challenge. One issue is the guidance on positioning them differs a lot between what your AVR manual might say and what might be recommended by source based layouts like Dolby. This can lead to confusion and poor results with different sources. Based on your AVR's manual it should be possible to place the speakers on the rear wall but if you go by Dolby recommended angles they would need to be placed on the side walls back a couple of meters from the couch.
Your AVR will do up to 7.2.2 with all 7 ear level speakers and 2 height speakers which could be Front Presence or in ceiling Top Front speakers. You can also consider doing just 5.2.2 where you only have 5 normal speakers and 2 height/ceiling speakers. Yamaha have quite good support for their height speakers with lots of options for many different DSP modes that control how they function. And with Atmos/DTS:X enabled content you can get them to output height info. Two of the smallest speakers that are a good match for your system could be used in the front top corners of the room or try in ceiling ones.
Also note your ceiling height is quite low which may cause some problems getting angles right. But it might also be an advantage for some speaker types like those bouncy atmos enabled speaker modules.
Here is a Dolby Atmos speaker layout guide I made which I have just modified to your rooms info from your PDF.
https://docs.google.com/spreadsheets/d/16PDbOdceFWBZ0zu7nsk5qFOzJofbo3440n6elHJ7w2U
There are a couple of measurements I have had to estimate which may need adjusting like your listening ear height and the position of your front speakers. Its main purpose is to give you some idea of where to place your height speakers to fall within the Dolby recommended specifications. But remember your AVR may have different ideas on where to place them. Look for the light green areas in some of the spreadsheets tabs where it will let you adjust the measurements that I may have got wrong.
It has a few graphs that show the layout of your room with possible positions and lower down has sections detailing specifics for each speaker placement.