Okay, I've played against both of these characters and I will completely agree that they are irritating. However, we've got some tools at our disposal. All of the advice I'm going to provide is going to be quite general since I'm not familiar with your style or the style of your opponent. If you could provide videos, I think I would be able to provide better critiques, but that's up to you.
Samus
Her missiles are a pain in the tucas, no doubt about that. However, you can aerial/attack right through them. Peach's bair makes this exceedingly easy given the range at which it juts out from her body. Beyond that, you're gonna wanna watch your opponent for specific patterns they're employing. If you've got a pattern, you've got something to exploit. It's not as easy as it sounds, but it's a start. You find a pattern and you try something to get around it. If that isn't successful, try something else.
Additionally, you'll want to space your attacks on Samus very well since she has her up-b OoS. On the other hand, you should rarely ever be grabbed by Samus, since her grab is ludicrously slow. Depending on how far away from her you are, you can run away from it on reaction and then dart back in and punish her.
Also, while her grab is slow, Samus, strictly speaking, is not. You'll have to be very careful about pulling your turnips because she can interrupt that relatively easily. She can, of course, shoot you with either a charge shot or missiles or she can run/wd in and hit you with a d-tilt, d-smash, forward smash, f-tilt, or dash attack.
Ultimately, it is my belief that this matchup is a headache because we can't do our Peach things with impunity as we can against other characters. We have to be significantly more careful because Samus is heavy enough that trading is more in her favor than ours. Furthermore, she can pressure us to recover low, which is not ideal for us since we have terrible options off the ledge.
I'll give my impressions of Link later.
