120 - 100 = 20 Orbs

Reinhardt can work as normal, in my opinion. 32 attack (if Attack bane) with Hone Cavalry gives you 38.

Leif might just have to work similar to units like Felicia: Relying on special triggers for success. You can give him an Attack +3 seal to offset the bane, so there's that.

I have no idea what you can do for Celica, to be honest. I've never gotten her.

This depends partially on your playstyle, but for Leif I think Death Blow or Fury would work, since his Spd will be at a crazy 41, leaving you room to focus on his Atk. Fury is especially good for chain maps like TT/CC since his prf B skill will restore his HP. Like Krazytre said, an Atk+ seal will help fix his bane, too, but I know from using Nephenee that 45 Atk paired with high Spd is perfectly fine. Moonbow is definitely his best special in this case, especially with his prf B skill.

Fellica can run a number of things, but I like the idea of Life and Death on her, since it gives her 56 Atk/37 Spd and she'll be sitting at a good 28 Def (and an even better 32 at 100% HP). Chill Spd helps offset that Spd regardless, though you might want to run Renewal if you don't give her a healing special/Aether/healer teammate. Other options include Darting Blow, Swift Sparrow (if you have a spare), and Fury (but definitely run Renewal with that). You might even consider Wind/Watersweep (and Phantom Spd) with Life and Death, since after 100% HP she'll have higher Spd than a large majority of units but not enough to double many common threats.

WT!Rein is so busted that even +Spd -Atk can't stop him. Just give him Moonbow, Distant Counter (if you have it) or Death Blow, and Vantage or a breaker skill and you'll be fine. If anything, his +Spd boon will help him avoid some doubles.