A couple of thoughts:
Your room is not large enough for two TVs. Your speakers dont have breathing room, are too close to multiple reflective surfaces and have an inconsistent environment for them to work optimally. Open your front stage by moving furniture from the front of the room to either the back or back side walls. Acoustic performance is a balance between your room and display location, which makes putting your display in the exact center of the front wall the preferred location. Try to avoid anything between yourself and the speakers, including coffee tables directly in front of the seating. The idea is to cut down on reflections as much as possible. Avoid mounting speakers too close to any flat surface, namely side walls, ceiling or floor. If your room and configuration makes this unavoidable this will make acoustic treatments that much more critical.
Replace "Yamaha center speakers" with either a single Klipsch C-20 or a single Klipsch B-20 mounted vertically.
Subwoofer? Critical for a home theater, even a modest one. Ownership is critical but then so is proper placement.
Acoustic treatments. Your room is likely an acoustic nightmare but can be improved drastically without a huge outlay of money or time and with some simple rearranging. Replace furniture in corners with bass traps and treat first reflection points at a minimum. Youtube is a great source for how to create your own acoustic treatments if youre on a tight budget and have very basic skills. Some of these are a little long, and a little slow, but I recommend you watch all these videos on what acoustic treatments can mean to you...
Last, and should be least on your list of priorities, replace "couple back speakers" with a pair of Klipsch B-20. This can wait till everything else is complete (namely your front stage corrections) but should be on the list regardless. Your ultimate goal is the same speakers all the way around. This includes a matching center channel if you can fit a traditional matching vertical-oriented center to match your mains (which are vertically-oriented). A C-20 and four B-20s will be good, and a reasonable compromise, but a five B-20s configuration is technically the best configuration possible.
One final thought...Your room is a challenge but thats mainly because it simply has too much stuff in it which ultimately affects both the look and performance of your system. Try to clear clutter, orient your system to the center of the room and be mindful of reflective surfaces.