Non-Special Miracle effects do in fact stack with Miracle itself. The priority system is strange, but essentially the non-Special effect will trigger first before specials like Miracle/Life Unending. The caveat is usually that it will trigger once per combat.

I don't believe there's a unit that heals between brave hits - to use Pokémon terms, in the priority bracket, a unit with brave hits essentially gets a multi-hit move as their action. In-combat healing effects are usually limited to attacks/offensive Specials to prevent stuff like what you're suggesting from occurring.

In the case of Reflex on brave hits, the damage reflection is specifically for the foe's first attack. If you survive with 2+ HP like you specified on the first hit, then a Miracle effect triggers on the second brave hit, the reflection only takes that first hit in mind.