You mean the vampire spawn who has to do the bidding of his master to lure in victims?
Yes, that one ... what story-wise makes him Rogue?
Show up on public event ... seduce (his word not mine) some noble out ... bring them to your master lair ...
Sounds like Bard to me.
What paladin code could he possibly follow?
Any ofcourse.
Have you talked with First Oathbreaker?
The NPC that unlocks this subclass for you.
You know what was his oath?
To follow his master and obey him in ever comand. Sounds familiar?
Also ...
Just out of curiosity, who said the he WAS paladin all along?

It may come as surprise to you, but you can sworn an oath any time you want.

Gale kinda needs to be a wizard for his story to make sense.
Nope ...
Gale need to be FORMER Wizard ...
His tadpole/orb/whathever excuse you want ... drained him to level 1 ... it might aswell drained him to "not a Wizard anymore"

:P
and Wyll should be a warlock instead of a cleric where he git power from a different source already.
All that is said in Wylls story is that he made an pact with Devil ...
So does Gale if you refuse to feed him with items ... does Gale becime Warlock? No?
So does that Paladin and his friends on Risen Road ... does they all become Warlocks? No?
So why should Wyll?
And shadowheart kinda needs to be a cleric of Shar and not the cleric of another deity.
Nah ...
Shafowheart only needs to worship Shar ...
There is no need for her to be Cleric.

Also we are talikng here about Class ... deity is completely different choice.

Either she is Cleric > and she worships Shar
Or ahe is not a Cleric > and she worships Shar
See? Easy, simple, effective, with scent of lemons.
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I answered your questions ...
Will you do the same?