There were a lot of instances where you messed up tech / spacing and got grabbed (aka lost the stock). Work on those little things and you won't get grabbed. That guy's grab game actually seemed super weak- just the fact that if he DID manage to get a grab, his wobble game was really good. Be careful about IC's in shield. It's nice because if you mis-space something, you won't necessarily get grabbed because their traction is so low (but you HAVE to not fast fall it, as weird as that sounds), but you have to be careful about the WD OOS --> jab --> grab. Not a guaranteed combo, but hard to avoid, especially if you're not expecting it. As popo, he also tended to roll a lot after a fair on shield. Keep an eye out here.
Same thing as for luigi- retreating fair --> jab / low ftilt works wonders for walling them out. Against an opponent with a strong grab game, I actually really like to camp platforms and drop down with aerials. It especially works against IC's because they're upward-oriented aerials aren't great. I think that would've worked well for you here. This guy especially seemed to like the ground game (as do many IC's), executing lots of dash attacks and dsmashes, etc. and not opting to go for up airs even when you were wavelanding on platforms.
As for splitting them: because of the frame delay on popo's vs. nana's shield, side-b and down-b actually work really well here. Eddie taught me this one and lord knows the man knows how to fight the climbers. Don't be afraid to go after nana if you ever get a jab or something that gets her off stage. Once you're off, popo can dsmash, fsmash... and that's about it. And those moves are super easy to tech too. Even if you don't tech it, you can usually DI it and come back as ganon.
Don't fall for blizzard shenanigans. That's a really good way to get grabbed.
edit: also, I would classify n0ne and kage both as ganon / falcon dual mains and trail an IC / ganon dual main.