How exactly are they winning in neutral? As a general rule, you're going to have to call/cover movement choices and options, or get into certain ranges where you can just do moves to beat certain options.
Are they lasering to force an approach then punishing the approach? Run, or walk up, ready to cover pre-emptive attacks, keep advancing or wait if they do nothing, try to get a grab (at least at lower percents). Over shoot the grab on a dash dance if they aren't fox trotting back multiple times, and if they are, just run them into the corner, crouch when you're comfortably close, and utilt or uair to catch a jump, dsmash if they stay to the ground, or grab. If they aren't crouch cancelling but keep moving, run up jab is low commitment, and if they actually think they can punish the first jab, you can probably get the second, but only do it when they come back in, and beware of moves like usmash.
Are they attacking relentlessly and beating out whatever you do to defend? If they're jumping super close, you can ftilt them out of it, and if they're shorthopping with something that's not drill, at the worst, you'd trade favorably with dsmash, especially when farther, but if they're coming from farther, dash or wavedash back and grab it. You can also crouch under the closer aerials, and CC the higher ones. In the event of ftilt, try to shield DI in and grab. You can also spotdodge almost all of these if you do it early enough and punish. If you're not concerned with getting a punish, you can roll in whichever direction sets you farthest from where they will be actionable at the end of their move, or if they're doing something laggy enough that they couldn't catch you either way, you could take the direction for better stage position.
Are they dashdancing a lot to bait out moves and punish? Needle, or, walk forward until you can hit them. This makes it easier to react to them trying to hit your advance, and you might catch them shielding or spotdodging with any kind of movement forward, like if you dash attacked or dash grabbed.
For Falco, is he doing laser->aerial/tilt/grab? If laser-> aerial, you can block the laser and wavedash immediately and whiff punish the aerial, but try to do this in reaction to the jump so that you don't just get lasered continuously. If laser->tilt, try to DI in and grab the tilt, or get closer when they're lasering and hit them out of the jump (or if near the ledge, grab so they grab break and go flying). If laser->grab, you can absolutely hit them before they land at the ranges that should work at.
For Fox. Expect a lot of dash dances and grabs. A well timed spotdodge can allow you to punish most of the more common approaches. Being smart with OoS, knowing when you can punish something and not challenging when you can't, but always acting immediately when not in a frame trap are important. But try to avoid doing either as much as possible. You can usually challenge his approach with ftilt or dsmash or movement when he's staying low, and if he ever fullhops, you can make him suffer from utilt or uair. Rising uair (try to hit with the tip of the initial hitbox, and later in the strong hit if possible) to nair can lead into a lot of things, like grab dsmash or ftilt at lower percents, and dash attack and grab at more mid percents. Fullhop the uair if not from a platform you're going to land lower than. Challenging Fox from below is much better than against Falco, but you can also just position yourself so they can't hit you coming down and punish their landing from their.
Get them offstage early if possible.
