From my limited experience vs ICs:
Don't stay on the ground too much, use platforms a lot and try to poke him with fair / bair. Even if he shields it, that's good for you, because it's keeping him on the defensive, and a lot of times you can shield poke or nana's shield won't come out in time.
Always be conscious of the range of space they can zone with wavedash -> grab / dsmash. Don't spend too much time there, or if you do try to bait the WD and punish with jumping out of the way -> dair or something. If you messed up and they got up in your face, JAB! It will beat their grab. It will lose to dsmash, but grab is much, much scarier. If you mess up and think you will get hit, make sure your DI is good for dsmash, and if you get grabbed by god start mashing as fast as you can. Every time you get grabbed it's a kill opportunity for them, and every time you get out you basically get that stock back.
Once you get them separated, start whacking them. If you are hitting nana, be able to turn around and hit popo at the last second if he is coming to get you off her, just be quick / sneaky about it. Uair and bair are good in these situations.
I suggest NOT doing sideB / downB really at all in this MU, because there are easier ways to get hits and it's super risky. Also in general, wavelanding away can get you out of some dangerous spacing if for example you're coming down and already used your double jump but are close enough to potentially get grabbed upon landing.
Play patient & cautious. Don't get grabbed, and make note of the setups that your particular opponent likes to use to get them. Poke with aerials. Ban FD. Good luck
Feel free to override any of this with advice from more successful players.
Don't stay on the ground too much, use platforms a lot and try to poke him with fair / bair. Even if he shields it, that's good for you, because it's keeping him on the defensive, and a lot of times you can shield poke or nana's shield won't come out in time.
Always be conscious of the range of space they can zone with wavedash -> grab / dsmash. Don't spend too much time there, or if you do try to bait the WD and punish with jumping out of the way -> dair or something. If you messed up and they got up in your face, JAB! It will beat their grab. It will lose to dsmash, but grab is much, much scarier. If you mess up and think you will get hit, make sure your DI is good for dsmash, and if you get grabbed by god start mashing as fast as you can. Every time you get grabbed it's a kill opportunity for them, and every time you get out you basically get that stock back.
Once you get them separated, start whacking them. If you are hitting nana, be able to turn around and hit popo at the last second if he is coming to get you off her, just be quick / sneaky about it. Uair and bair are good in these situations.
I suggest NOT doing sideB / downB really at all in this MU, because there are easier ways to get hits and it's super risky. Also in general, wavelanding away can get you out of some dangerous spacing if for example you're coming down and already used your double jump but are close enough to potentially get grabbed upon landing.
Play patient & cautious. Don't get grabbed, and make note of the setups that your particular opponent likes to use to get them. Poke with aerials. Ban FD. Good luck
Feel free to override any of this with advice from more successful players.