You play keep away with both of them. Olimar once you get in you figure out the situation. Can I keep going? Is he going for a gtfo move, an airdodge, spotdodge/roll/etc? Like once you get in on Olimar in certain situations, he gets REALLY boned even if you are just doing relatively safe ****. He's not lagless enough with his gtfo moves in these spots to be as safe as he wants to be. If you do something like Dair Nair shield (assuming he's a tad in the air and close to you after this knockback), he is in an awful spot. He loses for doing attacks, he probably won't be able to drift away and avoid a shield grab, Jumping over you isn't safe either, and you still have OOS aerials to think about. Fart charged, hit at 30% send him offstage maybe kill some pikmin, BAM awful **** for him lol.
Diddy is much harder to pressure and effectively corner. Diddy is more mobile and can zone Wario more effectively than Olimar can (and doesn't have to worry about Pikmin/priority ****ing him over). It's fairly momentum based and good Diddy players won't get greedy on trying to damage Wario. He has a fairly safe setup against Wario and he wants to play the RPS game over and over where you are slightly disadvantaged in trying to get in. Wario wants to win the RPS a few times, and max out the damage he can safely get and hopefully back off with a lead. Diddy can't usually pressure Wario into bad spots onstage, but he can force him to approach or limit how he can realistically get in. One big thing is to learn banana control defensively. Wario with a banana defensively is hard for Diddy to deal with because getting hit by the banana or having to maneuver around it to hit Wario, and assuming Wario is in a neutral/retreating position it's hard for Diddy to already be close enough to reliably snab the banana back. Z dropping, recatching with aerials, throwing it down, etc