I'm ok with respecing stats/ levels for the player character, maybe you decide along the way, that your warlock fits better with Pact of Tome instead of Pact of Blade or so. I'm concerned about changing race/class etc. alltogether. That would be too interrupting for me.
The companions are mo--capped to hell, there's no way they'll allow race respeccing for them.
My opinion: Gale Wizard through and through, shouldn't be allowed to respec class, but I personally hate that 15 in con. I'd like to change that Shadowheart. Only says she worships Shar, not a cleric (I think). Her backstory suggests she was picked for her skills in infiltration, maybe rogue, but her subclass more than covers this. Should be limited to Shar and trickery, with the option of rogue (but who in the right mind would pick that?). No other class or deity suits her backstory Wyll. Absolutely his first class should be fighter level 1 then fiend warlock level 2. These should be the canon first 2 levels. He was a member of the flaming fist he would have had to wear the uniform and bear the weapon, there is no way he shouldn't have medium armour proficiencies and maybe martial weapons. His 13 dex just doesn't make sense either. A famous melee fighter in light armour with 13 dex? No way Astarion. Everything about his backstory suggests bard over rogue. He's technically not even able to enter houses without invitation and his whole deal should be about personal charm and deception as that is what he primarily did to his master's victims. The only reason he isn't bard because it wasn't in the game yet and high elfs make better rogues. His starting spells should include charm person and disguise self and everything about the voice actor and fancy dan starting armour shouts high charisma. He has totally the mannerisms and affectations of a 'luvvie' actor Laezel: Fighter, nothing else makes sense. Probably eldritch knight suits best lorewise. Most people will take battlemaster though