Stalker +2 more

If you're adding three characters from the NPC's of BGII, and you're starting off with PC of a stalker and an NPC sorceress, you need to figure out how you intend to play.

If you are going to powergame, you're going to want to add some beef. If you like paladins, Keldorn will do fine once you equip him with gauntlets of dexterity. If you want to go evil, Korgan is a great tank. Minsc is also a fine tank and has handy mace proficiencies for the mace of disruption. Mazzy also turns out to be a fairly decent tank as well (as long as you don't mind short swords).

If roleplaying is more in your thoughts, maybe take Valygar as a companion stalker. Keldorn still works from a roleplaying perspective if you are good, as does Minsc, and you can probably justify Korgan if you are neutral or evil.

You're going to need a thief (while not absolutely necessary, it makes life much easier). I'd suggest starting a F/T over a pure thief class because, by TOB, beef is the most important part of the game. The only decent thief character to pick up as an NPC is Jan, and some people can't stand the turnip stories. Beren wrote a walkthrough where Yoshimo and then Imoen were his thieves and, yes, you can get by with Imoen so long as she is suitably jacked up with devices and you don't want to backstab. Me, I love to backstab, so I leave Imoen to her own devices.

You don't necessarily need a cleric, but it's nice to have. Not many choices here, Anomen or Viconia depending on alignment. For TOB purposes, I'd pick Anomen because he's got some fighter levels and I tend to play good parties. Viconia's magic resistance is nice, so it's up to you.

Of course, you can ditch the cleric and just take a druid. Jaheira is generally fine and has the benefit of multi-classing as a fighter as well. If you get the shapeshifter rebalance mod, though, I highly recommend Cernd. He's a single class druid, so he hits super-spell casting status sooner, plus, as a greater werewolf, he's a tough fighter as well.

I personally can't stand either Nalia or Aerie, so I cannot recommend them. If you want a mage/cleric like Aerie, make your own, as your stats will probably be better if you take advantage of the re-rolling. Plus, no annoying whining from a self-created PC.

So, to sum up, this is what I would do if powergaming:

PC's - Stalker, F/T, F/C (probably both multi-over dual classed for TOB purposes and more HLA's).

NPC's - Tahshia (whatever her name is, the sorceress), Keldorn, Jaheira/Cernd.

This reduces the annoyance factor of Anomen, Minsc and Jan (all may feel free to chime in and flame me for calling your favorite NPC an annoyance), maximizes your beef, and still gets you enough offensive spell power with the sorceress and Jaheira's/Cernd's summons/insect spells to make it work throughout.

I cannot really comment on a roleplaying party because I do not know your style. If you want, fill that in and I'll reply.

 

Looks like I misread your post. You want to take a total of three characters through the game, PC plus two NPC's, right?

If so, we've got completely different things to talk about. I still think you need a thief, so I would ditch the stalker and make the PC a multi-class F/T. You get most, if not all, of the stalker benefits, more HLA's to chose from, and the much needed thieving abilities. (There's a lot of free experience to be reaped from disarming traps and opening locks and I think traps are going to play a larger role in the reduced size party. Also, I'd boost the character's detect illusion stat way up so the spellcasters don't need true sight.) This character can dual wield Celestial Fury and another sword of your choice for protections and stat boosting purposes.

As for the other two characters, I really think you're going to need some kind of mage or sorcerer. The NPC's are, in my opinion, not great for these purposes, but I've never played Tashia, so I cannot comment on her. One thing to consider with a three man/woman party is logistics of necessary abilities. For example, if you're dead set on the stalker, then I think you have to take Imoen because, tricked out, she can be an adequate thief. Otherwise, I prefer sorcerer class to straight mage because you really don't need that many spells per level and I prefer the flexibility of the sorcerer. Alternatively to Imoen and the sorceress, you can take Jan (and his turnips) as he is a good enough thief and mage to satisfy both in the half-sized party you propose. He'll level up faster than normal, so his dual classed nature won't have as much of an impact on his spell casting.

I think a cleric type is going to be more important with a reduced size party, as the damage will be more concentrated (especially with your mage character essentially being a non-combatant). (Oooh, wait, maybe ditch whatever mage you've got and take Sola - he's a F/M, right?)

Hate to say it, but Anomen may be your guy. He is decent as a fighter through almost all of SOA, progresses as a solo cleric, so gets the higher level spells faster, will vaporize undead that much faster, and can be given Crom and Flail of Ages to commit mayhem when he needs a boost at the end of SOA and through TOB.

To recap, I'd make the protagonist a F/T (wielding Celestial Fury and a long sword - but, maybe ultimately that cool axe from TOB) and I'd ultimately wind up with Sola (I think he gets some kind of moonblade or something and can wield other swords) and Anomen (Crom and flail of ages initially, with a switch off to mace of disruption when necessary and, ultimately, Crom plus the runehammer). That gives you an arcane spellcaster, divine spellcaster, thief, and three tanks. Powergaming anyone?