Holy cow man! That’s a tough room. I think what you’ve done so far is as good as you can. Moving forward, if that were my room, I would consider the locations you’ve marked. I would also consider a matching pair of bookshelf speakers. Either wall mount the left surround and put the right surround IN the bookshelf. Or wall mount the left surround, and also wall mount the right one on the little JUT out between the closet and bookshelf. As far as kids and BS speakers, my thoughts are that kids are trainable and can learn to leave things alone. Ymmv of course. Lol.
While I DO believe in having speakers from the same line at least, the problem is that the room and placement will still affect the FR. So in other words while it would be ideal, considering the rest of the room/acoustics/placement etc, it might be the least of the issues lol.
I would still pursue Atmos. What is the ceiling height? That would dictate how I went forward.