Table Talk
It's alright; I've got a few irons in the fire too, so we can just take it at our own pace.
Let's give those concepts code names, something like Journey Child for the first one and Bad Bandit for the other.
For the Journey Child, I'm imagining them to be some sort of full caster class, themed according to the plane of existence they were transported to: a sorcerer, a druid, pretty much any full caster. RP-wise, they'd be totally lost in the Underdark and worried about getting back to their family - even hoping that their family is still alive and nothing has happened to them - while at the same time grappling with their weak body. Maybe they actually aged in that other plane, and had some really great adventures, but none of it transferred when they came back to the Material Plane.
For Bad Bandit, I was imagining anything in a spectrum between Rogue and Warlock/other spellcaster. If we went full rogue, I would give them a cursed magic item, so they'd pretty much end up with some sort of cursed magic item some way or another. Also definitely a stealthy person regardless of class, in order to fit that "infamous thief" archetype. For roleplay, they'd be guilt-ridden over the death of their crew, and struggling to manage whatever dark desires the cursed magic item has.
We can go as heavy or as light into the details of builds as you want; maybe you just give me a general theme, and I can go from there, or maybe you feel like doing the level ups for all of the custom NPCs - it's up to you.