Pretty much for all these matches d-tilts will become your best friend. You do not want Falcon to grab you, instead use Roy's sword dance for baits followed by grabs into up-throws (most often a Falcon will try to retaliate with a d-air, which you can counter and destroy) When you get Falcon off the level; your only option to edge-guard is to neutral-B, so space accordingly.
Falco is mad difficult for me as well, but you can run under most of his lasers and go for up-throw chain-grabs into forward smashes, depending on the percent they'll go flying off the level, and most likely side-b back, in which case you can f-tilt or neutral-b. If they try to hit you with they're up-b simply counter it, and obliterated their stock.
Marth is difficult too, but he's not as hard as the others imo. Space him out with retreating f-airs and wavedash d-tilts, then when they pop into the air go for a neutral-a or b combo, to up-air. Grabs are top priority in this particular match-up as well. So make sure you d-throw and if they DI into you, go for the F-smash. For edgeguarding you're gonna have to be kinda careful, you can always surprise Marth while watching him you his side B, then running off and neutral-b him off. But sometimes it's just best to grab the legde or do the light shield Marth killer trick (hold z and then move the control stick in the direction you want to go)
Shiek is mad annoying but basically the Marth tactic I told you sorta works with her too. But given her weight distribution you're gonna have d-tilt and grab her as often as possible.
These are hard matches, but Marth and Falcon shouldn't be that hard. Just space and remember Roy's grabs are as good as Marth, and make sure to utilize his sword dance as often as possible. Good luck man.
