Against Fox/Falco, you should stray from flat stages. This is because, on a flat stage you can't do much against a laser, except, jump it, shield it, try to approach, throw a pikmin at it or let it hit you. None of those options are good and are usually what the other person wants. You might be able to fair it, but that would probably hurt your pikmin and you want them to live through puberty.
You should try going to stages with platforms. Depending on the character, you might wanna go to a small stage with platforms or maybe a larger one with platforms. Against Falco, if you're comfortable, you should try yoshi's, FoD or BF. If its to small and you find yourself getting pressured to much, try DL.
SIDE NOTE: What are you using to approach?
Against ROB, since he can't spam his projectiles like falco/fox, you might wanna try short hop side B and following up with a jab combo, tilts or a grab. This works best at mid range and low to mid %. Once the person is high enough to the point where they get knocked back, you'll want to do the pikmin slide or else you won't be able to follow up. You can try mixing in fairs as an approach as well. If they are above you, on a platform or something, you can try uair(for juggles), bair or nair(for combos/juggles).
I don't know much about the ROB MU since no one plays him, aside from JC.
I'm not to sure about everything you know, so I'll leave it at that. If you have anymore questions or some specific stuff, ask me on skype.
