[QUOTE=LastDanceSaloon]who should I dump in favour of a decent Mage?[/QUOTE]Edwin is surely the most powerful mage NPC (his amulet gives him bonus spell-boxes), but he's evil so you might prefer Nalia, Imoen, Aerie (Minsc's Witch), or Jan (the gnome). I've never understood why Nalia and Imoen were designed as such similar characters, but they both have interesting bits of story to enjoy while they're around, and as single-class mages they level up relatively quickly and get plenty of high-level spell boxes. Aerie is decent since she's the only mage (aside from Jan if he has the Use Any Item thief ability) able to use shields and helmets and the only cleric able to use the Robe of Veccna (Bonus Merchants needed) or Staff of the Magi; there's also plenty of fun to be had inserting cleric spells into mage-spell-sequencers. Jan has amusing dialogue and good thieving abilities (Belm+Kundane+Mislead+Backstabs = rofl), and I think his spell book always comes with Project Image (probably the most powerful mage spell), but he can't easily use Abi-Dalsim's Horrid Wilting or Summon Skeleton (These are probably what you'd want to be casting with your projected image). Since all the characters have strengths and weaknesses, you may as well stick with Aerie for this play through. If you are still in Chapter 2, then Aerie has some nice dialogue with Haer'Dalis (the Bard. Having these two together will remove some dialogue options, so consider this duo for another time).
Personally I'd keep your current party, it looks fun. Don't forget to abuse Yoshimo's special traps ability by casting just far enough away that enemies can't see him do it, but close enough that it explodes and hurts/holds/kills all of them, like a stunningly-strong enemy-specific FireBall.
[QUOTE=LastDanceSaloon]Is the Bard better than Yashimo for roguing[/QUOTE]No, in BG2 a Bard's only thievery is pick pockets. Haer'Dalis is a type of bard that doesn't get to sing well until he gets a high-level ability. He can fight well, but his THAC0 isn't great unless he's using Mislead (+4 THAC0... also, his Mislead-clones can sing for the party, which is game-breakingly powerful). Bards are nice for their high Lore (item identification), high spell-level (stronger Fireballs, earlier Skeleton Warriors, etc), and slightly improved THAC0 (unlike Mages, their Melf's Minute Meteors hit quite often).
If you eventually lose Yoshimo, then any of the thief/mage options are fine, but you should start saving items (some rings, potions of +3Dex, etc) that boost thief skills (at least for dealing with traps/locks). It's not that critical though, since high strength (Cleric's Holy Power + Draw Upon Holy Might or Righteous Magic) will break most (all?) locks, and you'll get items to regenerate any HP lost to traps.
[QUOTE=LastDanceSaloon]Will I find any tanks in the 'good' branch who will be better than the one's I've got or am I now set in this regard? ... [I need] to avoid all the confusions, stuns, chaotics, beserks, Holds, etc etc etc[/QUOTE]Keldorn is pretty decent with the bracers that raise his Dexterity to 18. If he's closest to an enemy spell caster, they will futilely cast spells like Charm and Hold-person on him, and later items give him upwards of 50% magic resistance (so he's a good spell-tank). If you've got time to buff, then you can always convert a mage to a tank via the weapon-protection spells (surely the fight will be over before the 4 or so rounds that these spells last. Summoned skeletons are immune to all the spells quoted above, and they can be cast beside the enemy spell casters so they're sure to be the targets of the spells. Skeleton Warriors (when you're level 15) are fantastic tanks (their weapons count as +3, they're immune to normal weapons and several spells, and have around 40% magic resistance). Minsc (in D&D all rangers start with a free dual-wield proficiency, which many players complained was lacking in BG1) is alright for tanking mages when he's alone and berserked. When you start finding weapons that give him immunities, then his affinity for dual-wielding can make him extra resistant. Also, consider giving Minsc a point or two in Katanas for when you find Celestial Fury (it's stun effect works against the Spell saving throw, so it's very good against enemy fighters and clerics), alternatively you can later find a character to replace Minsc that already likes Katanas (but his hitpoints and personality are not as nice as Minsc's).