+HP -Atk Zelgius, +HP -Spd King Chrom, And -Atk +HP S!Tana

+HP/-Atk Tana is fine. She gains attack when she's at 100% HP with her Fruit of Iðunn tome, or you could give her a Bladetome if you really want to.

+HP/-Atk Zelgius isn't really that much of an issue if I recall. Even with an attack bane and Alondite, his attack reaches 49, and that's before other skills and ally buffs, and he still has a lot of defense that you can use to your advantage as far as tanking hits.

+HP/-Spd Chrom gains +5 to his stats whenever he's at less than 100% HP, and it's an invisible buff. Combine that with the +7 stat increase from Brazen Atk/Spd, and he'd be gaining +12 to his speed, having him sit at 36, or you could use something else like Brazen Atk/Def and then give him Quick Riposte.

Well, Tana is just as good as any other unit if you give her Blade, but if you want to keep her normal Tome she can still work. Just slap Fury and the Attack seal on her and she's just fine, especially when you factor in flier buffs (If you plan to use her there).

Zelgius is a little harder, but you can just keep Fierce stance on him and his attack output is fine honestly. And even if you did want to put Steady Breath on him, it would be fine. Black Luna makes his attack mostly​ irrelevant for those sets.

Chrom, is basically no different than a Chrom with any other IVs. I wouldn't recommend building him for speed regardless, even with the +5 speed from Sealed Falcion. He's fine doing what his other form has always done: Nuking dragons.

Even though the IVs aren't amazing, these units are so good as it is that it doesn't matter all that much