Well I'm not an expert but you seem desperate and i think this will work, if I'm right one button makes you go forward one for backward and others should either brake left or right motor to turn. When no buttons are pushed it should be in brake mode. It also shouldn't explode if you mash all the buttons lol. I would have wired it up on my bread board to try it out but don't really have room to drag my electronics stuff out right now. Depending on the relays you might need something other than a normal npn transistor driveing the coils on the relays. If this is way off someone please correct it before he blows his house up lol. its eight resistors, 4 pnp transistors, 4 npn transistors, 4 diodes, and 4 single pole double through relays. Like I said I'm not an expert I'm still learning.