I'm a multiclassed fighter/mage and i have just taken over nalia's keep, reason:becos she left my party when i decline, but i think i would prefer the mage stronghold is it possible to renounce your ownership if the fighter hold and then take control of the mage one?

2nd and last question,i have 2 cha slots in my paty and i have 2 choose between the drow cleric,anomen , and the bounty hunter , any opinion on who to choose would be welcome, thx.

As for the stronghold, if you really screw up to "rule" the keep then it will be taken from you again, and at that point you can do the mage stronghold quest (but I am not sure if Nalia will stay in your party after you lose the keep though...)

As for the party question, the best thing (and only smart thing also) to do is to take Anomen in your party because Yoshimo (the bounty hunter) will betray you later (figures) and for the drow cleric, she is a complete screw-up (sorry for the fans of Viconia) and the only good thing about the drow cleric is that you can have a romance with her (good advice though, if you are from good alignment don't even trie to seduce Viconia, she will be a pain in the **s later on if you do) but that is the only "good" thing I can think of for Viconia...

what the #¤#¤ yoshimo betrays me and leaves my party? and the only other thief is a good
character? which i by the way think i acidently killed
shit my party is really going down it seems, i also managed to associate myself with bondhi
and killed the good evil mage, and also killed that dude down in the sewers.
Maybe i should just go ahead and replay the whole thing straight away im multiplayer mode.
Anyone know if its possible to take a singelplayer save file and alter it so that i can
load it in multiplayer mode?

I don't think that you can use a single player file and convert it to a multiplayer file; but I can give you some advice on your party formations as per alignment.

-Good alignment; Minsc (Ranger), Aerie (Mage/Cleric), Valygar (Stalker), Mazzy Fentan (Fighter), Keldorn (Inquisitor), or later on mayhaps Imoen (but she is kind of a screw up) or if you are up to it to complete the De'Arnise stronghold quest, maybe Nalia also.
-Neutral alignment; Anomen (Fighter/Cleric), Cernd (Shapeshifter), Jan Jansen (Thief/Illusionist), Haer'Dalis (Blade), Jaheira (Fighter/Druid).
-Evil alignment; Korgan (Fighter), Edwin (Conjurer) and Viconia (Cleric).

Note: because there are so little evil NPC's to join your party, I suggest filling up your ranks then with Haer'Dalis and Jan Jansen, because they have a chaotic neutral alignment.
2nd Note: be carefull about having Haer'Dalis and Jaheira in your party; if they fall inlove with each-other you will have to butcher Haer'Dalis then sooner or later; I did find a middle-solution though, if you refuse Jaheira during romances (like being blunt to her) there is a chance that Haer'Dalis will leave you allone.

As you can see for yourself, again good characters have all the advantages (like in BG1). Bioware really screwed up to make a balance between the alignments (again).