I think of going solo Sorcerer but probably more complex combination would be take Cleric too - just 2 characters - Sorcerer and Cleric - I think sorcerer can ba fighter in higher levels - with all the buffs ( tensers ect. ) and invisibilites he would be great and overpowered fighter - combined with Clerics spells .... how does this work ? Did someone play this ?

I don't know, but I do know that Clerics are really good in at least the first Icewind Dale, especially single-class Clerics who can level up high enough to destroy undead outright with their Turn Undead ability. There are tons of undead in the game!

Also, you should mention which game you are referring to.

I would personally take the duo, simply because it's fun to have a bit of variety. If you want a challenge, solo Sorcerer should definitely be doable without needing backup.

I'd say that advice holds for both IWD1 and IWD2; both classes are really awesome in both games.

Soloing a sorcerer won't be very difficult with the powerful spells available.

I would ask for all IW games - but probably yes, taking both characters would be more fun, more spells, more skills ...