Perhaps a combination of Ike/Marth/Lucina & DH/Pac-Man/Alph would make for one of the strongest anti-Flare Blitz spammer teams around? Surely a combination like that could topple even a Doublezard team! Folks like DH & Pac-Man can get their projectile walls out there to provide a shield for their teammate to retreat behind when a Flare Blitz comes. Said wall also sets up openings for the whole team to come over for the big punishes. Even if one of them breaks through the projectile walls, Ike or Marthcina could fend them off themselves with Counters.
Considering how more common Zards are going to be with not only Mewtwos roaming around, but also having gotten DTilt & FAir buffs, finding a great team setup to confront them with in FG Teams would be quite handy. That Flare Blitz itself got a 2-sided damage nerf as well should help us out.
As for Bike spam, one of the more consistent answers I've found for it have been quick & lingering shorthop aerials for knocking Wario off the bike. I've mentioned a few folks already, but here's some more possible recruits for the anti-Bike squad with notable aerials: Mario, Dr. Mario, Luigi, Yoshi, Link, Ness, (Dark) Pit, Charizard, Pikachu
I'm thankful Double Spamuses aren't that common.... *sighs loudly, thinking of the last time he ran into one as DH with a Rosalina ally, and shivers* One dog's not enough to contain them....
To continue the list of gripes that actually relates to the rest of my post, teammates that merely dodge certain long-range attacks (ex. Charizard's Flare Blitz, Bowser Jr.'s Side B, Wario's Bike, etc.) instead of stuffing them (exceptions being moves like Thoron or ROB's Lasers when no one with Reflectors or Absorbers are on the field), leaving the partner to deal with it and potentially get KO'd by it. This isn't like 1v1 or even FFA, where the threat is over as soon as you dodge or block it. If you're in FG or even FF Teams, it's not enough to avoid it yourself. You've got a responsibility to stuff those moves whenever possible to protect your team, especially if your ally's someone like Lucario, King Dedede, or Jr, who benefit greatly from rage. Some characters like DH, Jr, and Pac-Man are better at this than others, I'll admit, but you've got to at least try, even if you may get damaged or even KO'd for it.