*dusts off Fox knowledge*
Okay, where do I start?
Does it stand to say, Iblis that your Fox looks very stiff? There are time where you just stand there and your moves are choreographed because of it, makes you easy to predict, not as good as when we first fought each other waay back, where you were fluid with your moves, making it hard to know what to do next against you.
That Marth wasn't very good, as marth has a 0-25 cg on Fox, with a tipped forward smash to chase. His spacing was okay, but his pokes needed work. Also, he didn't capitalize on Marth's edge guarding game as well as he could.
A few things you should work on.
First keep moving, Fox is a fast character, do fast things, run, short hops, anything. When you're just standing there, your Fox looks sporadic and jumpy.
Learn more mix ups. You were doing the same thing a lot, which didn't compliment your predictability very well. But I can understand that it's vs Marth, so your options were limited to an extent, but you could have done something different.
Practice your JC Up smash OoS, I see many situations where that would have shut Marth's *** up, especially during his Dancing Blade. On the note of Up smash.
Use it more early %s on.
It good damage and since you're doing it early, you'll more than likely get rid of it's stale negation with other attacks to killing percentage, and perhaps even get a fresh bonus for that extra stretch.
Finally, try and grow accustomed to instant shielding. For obvious reasons, that'll help you a lot in this match up more so than it would others.
As for ZSS (Which you named Fox vs Marth 2 by the way), your stiffness bit you in the *** here, your opponent seemed to have hit you a lot where you just be dancing like a hopped up rodent. You also didn't camp in this match as much as you should, you always just dived in there. ZSS doesn't have good approaches, so camping was going to do some good here.
ZSS' crouch camping would only have helped her more so than it would oppose you, plus you still have the advanntage.
Again, JC Up smash OoS would have saved a lot of trouble, especially when he was spamming down smash.
ZSS has poor recovery options, use that to capitalize on Fox's edge guarding, a good ZSS will never attempt a recovery below the stage, force her.
Still, the biggest issue if you fluidity, work on that first.
Zelda...don't know what to say here.
Camp more, much more, you ran into a lot of damage willingly. Zelda isn't an approaching character, Zelda is a bait, poke and punish kind of girl, camping would put you in an advantageous position.
Zelda also does not have that good of an edge guarding game, which perplexes me to why she kept you at bay for so long. You (and Iblis for that matter) need to go back to basics with recovery, Fox copters are cute, but shine stalling would have helped more, I've seen you do it a few times, which is nice, but do it more.
Learn to SDI better, Zelda is made of multihitters, try to save yourself some damage by mashing out, especially her up smash.
Do more neutral airs (you too Iblis).
Jenks, your biggest issue is that you don't camp, which always seem to come back and bite you in the ***. At least camp a little. Like I said to Ibis, try for an early Up smash, camping will help fresh this move out, as well as down airs.
For Peach, don't know, your friend doesn't play a noteworthy Peach, so the best advice I can give you is to not be on the ground so much. Peach's air to ground game is way better than her air to air game, you at least stand a chance up with her. Camp more, those first few seconds were a joke, so I'm even not counting that.
Try and upload some offline matches, since you want critique, it'd be best for us to observe you at your best, so we'll know what your real high and low points are, as with wifi, those points are clouded with lag johns.
i agree with light on the smash DI thing with zelda
...on another note ^^^daym!!! ignore wat i said, he clearly just wins