I still think bad to have both becs connected to rx - i think you should pull one red wire and turn both switches on.

I also think you have one motor going in the wrong direction - I suggest changing two wires on one of the VXLs.

One motor needs to be reversed due to it facing the opposite direction to the other- hence why the stock erevo (brushed) has one special reversed titan motor (wiggle your fingers in the air and pretend they are motors and the spur, you'll soon see...).

Follow these guys advice, there is something wrong in your set up.... I run twin MMM with out an issue, and its all thanks to these gentle men.

you said random flashing, what you mean?
red, green, red, green, red, green, red, green? mine did that, and it fried :/
just ditch the dual vxl and get a MMM if you can, dual vxl killed my both escs and i ruined one motor

Here's a simple sollution.....Take both velineon systems out......sell them on ebay, prolly get about $125 or so each (just an estimate), buy a MMM combo and be done!