I just arrived at Berengost and I wish to have all caster party: clerics, druids, mages, multi and dual class like cleric/ranger. But no pure rangers or paladins.

Problem is that I never got past Berengost and I'm not familiar with npc...
Also, no Edwin or other evil characters since I do full good casters run. Imoen is OK, since I plan to dual-class her.

Did you already pick up Jaheira from the Friendly Arm? (Fighter-Druid)
She comes with Khalid as a pair, but accidents happen (like him running into a pack of wolves all alone without weapons or armour).
Branwen is a cleric - she's at the Nashkel carnival.
Xan is a mage - Nashkel mines, right at the end.
Dynaheir (mage) can be rescued from the Gnoll fortress - if you pick up Minsc, he'll need to have an accident or she'll leave when he does.
Quayle (cleric-mage) is found at the entrance to Baldur's gate.

That makes 5 plus the PC

Edit: I almost forgot Yeslick (fighter-cleric) - he's in the Cloakwood mines - take him until you reach the city of Baldur's Gate and then decide how your team's doing and whether you'd prefer Quayle to take over from him or Branwen (or one of the others) or not.

https://pihwiki.bgforge.net/BG1_NPC_rundown (spoilers ahead)

If you're really gonna run this party, you're going to need to make Jaheira your tank. Get yourself some Ankheg Plate Mail early (there's a freebie hidden in the town of Nashkel, map coordinates 183, 2745), put it on her, and never take it off.

In Bereghost there is a guy named Garrick, do his quest the non-evil way to get a new party member option. With Jaheira in the party there is a timed quest to get to Nashkel and talk to the mayor there, afterwards you can do things without time pressure. At Nashkel carnival you might find another ally, talking in Nashkel to Minsc or Edwin will reveal where another optional party member can be found.

Is your PC a thief of some kind? Because if not, you need one in your party and IIRC there is no non-evil thief/mage or thief/cleric available, unless you take Imoen early on and dual class her to mage once her thieving skills are up to par.

Also, your party will kind of lack in offensive power since pure casters (even clerics or druids) suck at melee and don't have much in the way of nukes. Notably, the final boss has really high magic resistance, so killing him will be a pain with an all-caster party.

Anyway, I don't want to discourage you, but you should be aware that unlike in some other games, doing an all-caster group in BG is challenging and may be too hard for your first time playing the game.

I dig hearing about how others play my PC gaming favorites. Beatrice, your all-caster party sound fun. Why are you choosing to play BG this way?

If you're an experienced BG player, an all caster party may be a fun challenge, but if not you're likely to struggle mightily with one. Since you begin play at level 1, the more immediate concern is getting so called "tank" characters that can dish out and take melee damage. As was previously mentioned, your only early choice here is Jaheira, but her druid multiclass means she's never going to have a great hit point total. The best option is Yeslick, but he will not be available until the midpoint of the game. So, depending upon your own PC's build, Jaheira and Branwen are going to have to be your picks.

A more longer term concern is lack of a rogue for locks/traps. You should dual class Imoen at level 6 to maximize her mage abilities (or 7 to maximize her thief skills, but I recommend 6). However, you'll need another thief in the party to cover for her until she regains her rogue abilities. Unless your PC is a thief dual- or multiclass, you're out of luck here. There are no good or neutral caster/thieves in the game, and Shar-Teel (who is both evil and not a caster) is the only one that can dual class to a rogue.

This sort of party is going to be a lot more viable in BG2, but if you can make this work in BG1 without extreme frustration, then more power to you.

I'd probably fill out this party like so:

Jaheira and Branwen as front line characters (adding Yeslick when possible)
A F/M/T triple class for the main PC, or a F/M or F/C dual or multiclass
Dynaheir as the primary mage (or Neera if you have the Enhanced Edition)
Garrick (bard) as a support character (drop when Yeslick is available)
Imoen as described above.

I agree with others. If this is the first time you are planning to complete BG1 then using all caster party will be extremely challenging and difficult. It is a fun idea, but I would never recommend it to anyone but very experienced BG1 players.

The main issue is that mages/clerics are really squashy early on and they really lack offensive power. Jaheira is then a must for you as the main tank. She can do alright, but she will suffer from low hit points and it will be a problem before you get some good kit later on that will lower her Armor class sufficiently.

HanSewLow and I are of a mind on most respects.

F/M/T as your PC seems the best option. Triple classing hurts progression, but with lack luster fighter and thief options it just makes sense. I'd go half-elf for the extra HP. And Find Familiar as one of your starter spells (again, for the HP).

Front liners - Jaheira as tank, Branwen providing melee support. Later Yeslick as tank (shorty saves!), Jaheira as melee support and ditch Branwen. DEX gauntlets and a big shield for Yeslick, STR gauntlets and big staff for Jaheira.

Primary ranged - Imoen, dualled low, because you don't want to spend the whole game waiting for her to become useful, give her a nice shortbow. Garrick, not the best caster, but has rogue HP and Thac0, can use a a crossbow or longbow, wear armor, pickpocket and has great lore.

As for the final slot... Dynaheir (or Neera if you have BG:EE). If you have BG:EE, I'd eventually replace them with Quayle. Quayle is in original BG, but got tweaked in BG:EE and is much better. Quayle has reasonable DEX, can use helms and shields, and has shorty saves.