Most of the interpretations I've found suggest that the lower "Lobes" are actually front legs, with rear legs either hidden entirely behind them or as the upper lobes, with the leg bits folded behind them out of sight. This doesn't really sit well with me. I generally like having less humanoid aliens, and would enjoy the squat little waddling Melnorme, but the mouth ruins it for me, since their jaw would overlap with their legs. It makes me assume that this is just a head your seeing. Hopefully someone cleverer than me will be responsible if this ever becomes cannon.
No clue. To me they always looked like some rubber toy. Probably rounded on the bottom. I don't see hands, feet, etc. They just don't seem very capable of anything. They look more like a worn eraser head than an intelligent life form who evolved into a species capable of interstellar travel.