Of course you should pair him up with Cynthia.
Dual Support + is not going to outweigh putting Brady with his S-Support wife. The S-Support is crucial for enhancing Dual-Strike rates, which Dual Support + does not do.
Moreover, you get a double Galeforce pair with Brady/Cynthia, which gives them 3 attacks per turn (assuming they achieve kills, which they should).
Brady - Galeforce, Limit Breaker, Aggressor, _____-faire (where _____ represents the weapon type he is using primarily) and Luna.
Pavise and Dual Guard+ are almost pointless for this map. You can se the stats and abilities of the enemies, so you can always work out what is the worst case possible scenario in combat with a particular enemy and can thus avoid picking fights with anything that could kill you (having another unit better suited to fighting them fight them instead, or having unit get healed back up to a point they can survive the combat first).
And because you will likely want an abundance of staff bots, healing from them is plentiful AND you can easily reposition your units so that they don't ever get attacked on the enemy phase….. meaning that all combat will be combat initiated of your direct choice. Which means you don't need these chance based skills (Pavise and Dual Guard +) to help you survive as you'll always pick fights you KNOW that you WILL survive.
They aren't ENTIRELY useless, as if they do trigger they may prevent enough damage that they save a staffbot's turn that would be otherwise used on healing, but all in all they aren't reliable enough to make this worthwhile….. you're better off going for a guaranteed damage increase with a -faire. And while Luna isn't guaranteed either, if you're set up correctly you'll get 6 strikes against the enemy (2 from the front, 4 from the rear partner) before they can attack. Luna has the same chance of triggering as Pavise but will help you kill the enemy BEFORE it attacks (while with Pavise it can only trigger WHEN the enemy attacks). So Luna is really better for defensive purposes here under the "best defense is a good offense" philosophy. Dead enemy units cannot do any damage to you, after all.
And you have Limit Breaker. And if you beat the Normal Route once you'll gain access to a really good Rallybot.
Between Limit Breaker and Rallies your characters aren't going to be overly threatened by the Apotheosis enemies as long as you account for things like Vengeance, Luna, Aether, etc. before you initiate combat. Bring a calculator with you if you're worried you'll mess up on the mental math on figuring out how much extra damage these will cause.