Samus
You can't do anything about Samus' zair. The only thing that can deal with that is Pit's Mirror Shield, your regular shield and spotdodging. But even if you want to dodge it, you're bound to get hit by it. Her Missiles are the same way. Her Super Missiles are easier to avoid, but her Homing Missiles can get you. I assure you that it's easier to dodge those better than zair. But Samus can use both one after another, so basically you really can't do anything.
When you get close, you pretty much shut her down. However, she's got good tilts and her smashes have decent knock back. As for her floatiness and heavy weight, not much you can do there. A fresh back throw will not kill her instantly. People rely waaay too much on that. Her grab release can be blocked. You can shield it, but you never know when she's going to use it unless of course she continues doing it everytime she grabs you.
Her spike is pretty good. It comes out really quick and I love it a lot. There's not much you can do about that. Nair may be able to stop it, but that doesn't mean it'll never work, even if you do use nair against her dair.
Falco
I can't remember what SHDL is, but I'm thinking it's short hop dair? laser. Well, whatever it is, if he's trying to get you to use your PSI Magnet, don't. You're probably better off shielding that. I don't believe Ness can escape Falco's CG and if he can't, unless on wifi, don't bother doing anything. If he tries to get you off the stage, you're better off not doing anything, letting him dair you and then you can use your second jump. Someone probably has better advice for this, but whatever.
For his SH > Laser, use your PSI Magnet if he's at a distance. If he likes to follow it up with a Falco Phantasm, use your shield instead. If he's close to you doing this, use your shield. There is a possibility he could grab you, but there's also a possibility he might use his u-smash or f-smash. For his tilts, just do your regular procedure. SH > retreating fair. You really shouldn't let him get a chance using his tilts on you anyway.
Corrections are accepted. I usually find Falco easier to deal with more than Fox or Wolf.