For Astarion we got an Elf/Daywalking Thief with an arcane trickster option Abilities are also in flux here, but currently he has Str 8, Dex 17, Con 14, Int 13, Wis 13, Chr 10 he's reppin a dagger and a bow, and collar popping with padded armor He's the basic sneak-about and lock-buster. Not the best backstab for damage but he does have some bite, mainly operates at range though and for rogue utility like scouting.
For an alt sub, I think the natural might be to drop a Tiefling on us, Alfira might work, or even a Sazza if they let us roll with a goblin. The former more on the spellcasting/utility charmer line as a Bard, the latter more the sneak or cutpurse Thief line. I think the challenge with Astarion is that, despite being ghost white ex sanguine, he's got a lot of color in the personality and that rakish charm. So I think in a sub in you'd want an archetype with some dazzle sazzle to em. I do feel like we need some shorties even if it breaks phenotype, so Sazza might qualify there. Astarion presents as neutral-evilish and hypersexual, so it might be fun to see them go a similar route with Sazza. She strikes me as having the confidence and experience to lean into it with the cat calls, even if its not exactly what Tav is after.
I personally feel like Astarion is just begging to be multiclassed as a ranger or a fighter. His natural Dexterity is amazing and he can go meelee, ranged, or if they don't touch his WIS (they better not because I have plans for it) you may multi him into a cleric for the ultimate support character, picking locks, disarming traps, scouting, giving buffs, while still being amazing with a bow. I think Astarion's stats are as diverse as they are exactly because they are setting him up as the flexible support companion who can fill the gaps, whatever it is that you may need. in 5E, DEX based rogue/fighters are incredibly reliable damage dealers, but Astarion can become an AT, an Assassin, he can multi to ranger, fighter, cleric and wizard, and he is just a joy to have around. The only reason not to take him is if you can't stand his personality. If we must have a sub, we should have an evil bard to cover for Astarion. No clue who he might be, but I don't want a goodguy bard in my party, unless if it's the aforementioned dwarven skald.