I have problems with the falco matchup too so I'm no expert but here's some tips.
You can practice powershielding laser in 20xx in version 3.something I forget the exact number - not the most recent one. Probably just youtube that to find specifics.
There's multiple ways to deal with lasers but imo it's still pretty difficult and a very tight timing. There's an SSBMT vid going over 5 ways to beat laser besides powershielding and a recent one specifically going over take laser --> action which can be quite good. Personally, I get most use out of wave dashing back but I still get rekt by most good falcos so dunno how much that means.
I think in general the way to win the matchup is to punish very brutally. Whenever you get an opening/grab, they should be dead pretty much, or close. Practice your gimp setups ie down throw -> dtilt, dthrow -> drop zone fair.
In neutral I see some Marths like PewPewU use a good amount of approaching nair even though that's generally supposed to be bad. I'm not sure why exactly but I think it's better in this matchup. Also, you can call out lasers if you're close enough with dash attack, especially if they're lasering high.
For Fox, personally I find that matchup much easier, but basically get a grab and then combo the **** out of him. You can wall with in place nair but he's fast enough to punish that so don't spam it. Use safe dtilts to either get a poke and try to grab or use shallow dtilts to bait him into trying to punish, then grab him. You're "supposed" to play the matchup very grounded in general because he's fast enough to punish your aerial lag. I tried being a lot more grounded and just sticking to grab/dtilt/aerials only once in a while and I'm pretty sure I got significantly better results.
Good luck!