My current party consists of:

ME (Cavalier)
Keldorn
Minsc
Nalia
Imoen
Aerie

Can you guys give me some opinion on whom to take out?
I was thinking of getting rid of Nalia...

Also, I want to know what proficiencies should i invest upon when dual classing Kensai/Mage at lvl 13? Will i get to use swords or dual wield katanas after my mage lvl passes lvl 13?

Yep, do it. You've got a way better theif-mage in Imoen and Aerie's there for more magical backup, so drop Nalia after your done with all her quests.

As for proficiencies I recommend dual wielding, swords or katanas is up to you though I went with katanas (for the celestial fury).

Will a kensai/mage be able to use the celestial fury??? What about the staff of magi???Should i give it to him???If i drop Nalia,who should i pick up???She's the only mage i've got that can cast lvl 7 spells now, i just finished the asylum quest.

imo

get jan instead of nalia

My kensai dual-wields both katana's and longswords .. gives him a whole lot of swords to kill with :D
Long swords are very good in both SoA and ToB, the only reason i dual-wield katana's too, is because of Celestial Fury, and .. later on in ToB, Hindo's Doom ( gives protection from death-magic ).
Im thinking Hindo's Doom + Blackrazor is pretty nifty.

Staff of the magi is nice, but i think its a bit wasted on a kensai, he's a sword saint, respect that [img]smile.gif[/img]

A thief with "use any item ability" on the other hand, is very very lethal with the Staff of the Magi ( unlimited invisibility )

I say get rid of Keldorn.You are a palladin and can use carsomyr therefore Keldorn is of no use to you.
If you want another fighter try Valygar with the Celestial Fury.
Also don't see nalia as a thief mage.See her as a mage that can use thief weapons! :D

Dump Keldorn, as stated above you already are a Paladin, dump Nalia and Aerie.

That leaves you with

Cavalier
Imoen
Minsc
Mazzy as another Tank
Jaheria/Viconia Either will do as secondary tank..
This slot you could leave open for rotating NPC's to do their quests..

My party consists of

Tristam M/Cavalier
Demora Skald
Mazzy
Jaheira
Viconia
Yoshimo

Going to substitute Jahiera for whatever NPC comes along...

Just kicked butt on both dragons..although shadow dragon was cheesed to death, red dragon was lagitimate...

Whos Demora Scald?

I think it is a custom character made by Tanoch.

dump keldorn but not aeire, she is a good healer. Have her learn all healing spells (or mosttly healing spells) then set her script to go around and heal the party members. that way, in battle, when you are fighting she can stay back and heal when needed.