I need some help with my party so far I have

Me (Kensai, being dualed to Mage at level 13)
Minsc
Vironica
Jan
Korgan
and I need 1 more person.

Will anyone get into fights and leave?
Should I keep the party as it is or change some members?

Jaheira's pretty good.

Nobody in your party will fight, but Keldorn would fight with Viconia, and Aerie would leave because of Korgan. Aside from that, I think you can pick anyone and they'll get along well enough.

Friction is to be expected with such a diverse group, but as long as you keep your rep middling noone will leave. They might snipe or insult, but nothing will really come of it.

I would go with Edwin. Can't go wrong there either.

Jaheira. She can add more healing with her druidic spells and tank if necessary. She also has some of the best quest XP in the game.

Keep an eye on your reputation. Viconia and Korgan will leave when it gets too high (above 18) and Minsc needs it higher than 5 (iirc) to keep his ranger abilities.

Druid or Cleric - you're pretty weak on the "Divine" spells side. I'd say take Jaheira along, as she's better than your bog-standard druid 'cus she can use scimitars and better armour etc. You might also consider Anomen or Cernd. Anomen's a good fighter and has a pretty interesting side quest, whereas Cernd will advance to higher levels as he is single class.

Actually all druids can use scimitars but Jaheira is the best tank in the game, she is very defensive, can achieve best AC, best resistances, saving throws, with her ironskinsi buffs, summons, heals, she is one hard nut to crack! I love her!

Because of the nature of BG2, it's very difficult to have a middling reputation. If you don't want to occasionally do evil things to keep your score down, I'd rethink your party composition. Or just kill Nalia's aunt.

The Slayer change is a handy rep manager.