wiring three amps to two subs?

I believe MTX does have some amps that are strappable- check your manuals to be sure.  They will tell you what wiring configurations to use without any unnecessary (dangerous) guesswork.My ex once told me I have a perfect face for radio.

Can't do it.  You're trying to use gear that is mismatched to the task.  Suggest you sell the 250D's and buy one new mono amp.  Look for one that is capable of running a 1 ohm load at about 1000 watts.  That will be easier than trying to find one that outputs the target 800 watts at 1 ohm....but you'll have to be especially careful in the setup that you don't overpower the subs.  The option is to buy a two channel amp and bridge a total 4 ohm load onto it.  This would be the more expensive approach, most likely, and there again you're looking for 800 watts.  Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.