In my opinion, the Suzuki Study 32 is one of the easiest standard melodicas on which to bend notes. I believe that the flimsier and more fragile the reeds are, the easier it is to bend (and to damage the reeds, probably). Others may disagree. I’m a fan of the Study 32, and you might be interested to see this: https://melodicaworld.com/forums/topic/melodica-tracheotomy/
I have seen a couple of videos of Japanese players playing two melodicas at once. One or two might be linked here someplace. I don’t recall what kind of a setup they were using. Pianonymous would probably know. You might go browse around the plumbing section of a Home Depot or hardware store to see what kind of Ys they have. Or search for this on Amazon: Plastic Y Tube Connector Joiner Hose Pipe Fitting. You’d want something that fits into melodica tubing.