While it would certainly be nice if we could look at your pictures and easily determine the best placements for your subs, the fact of the matter is that no one can predict this with any degree of certainty. The key to optimizing multi-subwoofer systems is having the ability to measure the response, and using those measurements to guide placement and EQ, as well as timing optimization. Do you have any way to measure your response? Something that can measure in both the frequency and time domains is most beneficial, but short of that, basic frequency response measurements are a good place to start.
Having said that, there are a couple of models one can use to guide placement. The first is Welti/Toole's recommendation: http://www.harman.com/EN-US/OurCompany/Technologyleadership/Documents/White%20Papers/multsubs.pdf
For dual subs, the most optimal placements were found to be midwall, front and rear, with opposite corners being nearly as good. However, the Welti simulations, measurements and guidelines are based on a rectangular, sealed room. If the room does not meet those requirements, the recommendations are less applicable.
There is also the philosophy of Earl Geddes, who recommends random placement of multiple subs around the room: http://mehlau.net/audio/multisub_geddes/
However, his guidelines are based on statistics, and may not be applicable to your particular room and placement options. Also, they require more than 2 subs, with one being an LF sub and the other 2 being "filler" subs. Also, Geddes eschews Bass Management, (all speakers run as "Large" or Full Range), and his technique virtually requires measurements for optimization and level setting, (the 2 "filler" subs are set at lower levels than the LF sub, and the levels are optimized by measuring the response and setting them to the lowest level that impacts the response.
I, myself, use a hybrid of Earl Gedde technique. I have placed my subs randomly around my room. However, I use 3 identical subs, I use gain-matching for setting the levels, and I use Bass Management for bass redirection to the subwoofers. I use XTZ Room Analyzer to measure and optimize my subs. http://www.acousticfrontiers.com/XTZ-Room-Analyzer-II-Pro.html
I have posted my results here: http://www.avsforum.com/t/759877/seaton-sound-submersive1/4500#post_19446901
Bottom line, you can spend hours and hours moving your subs around your room. However, until you can measure and "see" your response, you are pretty much just guessing and hoping. And so is anyone else who makes recommendations of placements for your subs in your room.
One last thought... the listening position has as big an impact on what you hear as does the placement of the sub(s). From your pictures, it looks like your LIP may be very close to the middle of the room. The middle of the room is usually a broad null for bass. 1/3 or 2/3 of the long dimension would be much better than the middle. IOW, if your room is 24' long, placing your LP at 8' or 16' will be much better than 12'.