I've no idea how to make use of two different types of controllers that can't talk to each other. There are controllers that can be paralleled (MidNite Solar's KID is the one I'm aware of) but that would mean purchasing two expensive controllers just to make use of a 50W panel .. not worth it.
So... If it's not reasonable/practical to make use of two controllers...
A) If you run the 2 120W panels in series, the VoC is too different from that of the 50W panel, so you can't use the 50W panel. Use the 240W available, and be happy.
Upside: Easy, efficient.
Downside: You lose 50W.
B) If the VoC of the 50W and the 120W panels is reasonably close, you can parallel all three. Just combine them as close to the controller as reasonably possible in order to lower the line losses. (In this case, MPPT didn't get you anything - a PWM would have worked fine. Chalk it up as a learning experience. :) ) Enjoy the 290W, and be happy.
Upside: All available wattage is used from existing panels.
Downside: Money spent on the MPPT controller was possibly wasted.
C) Sell all the panels and replace them with new identical panels that fit, wire them in series, make full use of the nice controller, and be happy.
Upside: New panels are more efficient - might be able to get more than 240W in the same amount of real estate.
Downside: Expensive.
Sometimes there is no perfectly optimal solution and one just has to pick.
