Jumbl SINSB7W ProGrip Ultra Stainless Steel Speaker Wall Mount Bracket White, Pair of 2 - Thread Size: 1/4-20 - Holds up to 10 Lbs | Adjustable 2-pack speaker wall mounts for satellite, bookshelf, cube & surround sound speakers with 1/4-20 thread

I get it. I use these because they blend very well and are very capable despite their size. In-ceiling speakers at the rear might be a problem if they don't give enough adjustability to overcome the slant away from where you want to aim them. https://www.orbaudio.com/products/quick-pack I would use a mount like this rather than the ones from Orb https://www.amazon.com/dp/B081QPYXM7

I use these in a bigger room than yours and they work great. https://www.orbaudio.com/ Pretty easy to fit most anywhere and sound great, much better than you'd expect. I'm not a fan of their mounting brackets especially for a vertical wall, but there are plenty of other options like these? https://www.amazon.com/dp/B081QPYXM7