I have done a number of movesets with Chrom and Lucina. They would be a team far unlike the others. They share a health amount, but the way they fight together is different.
Ice Climbers scarcely actually function as a team, so much as one character mimics the other. They are interchangeable
Zelda and Sheik are two characters who have absolutely 0 synergy and no reason to be paired.
Pokemon Trainer isn't a team. It is just a step further into mediocrity from where Zelda and Sheik left off. Instead of rewarding you for actively using all the Pokemon, you are needlessly penalized if you don't.
Olimar is an ammunition based character.
Rosalina falls under the puppet-fighter archetypes. We'll see how she pans out.
None of these teams really call in assists like you would in a fighter, and I think there is a lot of untapped potential.
In my movesets, the supporting character would be in the background, and all of the Specials rely on the supporting character. For example:
B: Swap
Switch Chrom or Lucina. Can be done mid-attack, allowing the supporting character to continue a combo string.
B Forward: Dual Strike
Supporting character jumps in to attack. Lucina does a multi-hitting stab, good for combo setups. Chrom does a leaping slash, good for ending combos. This move has no animation for the active character, so it doesn't interrupt your offence.
B Down: Dual Guard
Active character blocks the attack, and the supporting character jumps in to attack while the opponent is off-balance, taking the role of the active character.
B Up: Aether
The active character throws Falchion up and exits to the background. The other character plants their Falchion into the ground, jumps in to catch the airborne Falchion and brings it down.
And so on. I have made more than one moveset for both Chrom and Lucina, and I can continue to do so. It is silly to assume they would have to fight the same way, because there are still myriads of fighting styles left to be explored. The fact they both use the same sword enhances their potential.