My party currently consists of me (fighter) Minsc, Jaheira, Keldorn, Yoshimo and Nalia however I have now come across Aerie and from reading messages already posted she sounds good. Therefore question is do I take her on and if so who do I drop?.

I think your group is fine as it is already, and Aerie is a bit overrated - her HPs are low and her leveling up is slow. If you want a good cleric get Viconia. If you want a good mage, Edwin. (They're both evil but don't let that stop you.) You already have an adequate mage in Nalia and a healer in Jaheira. BUT if you want the romance, then I'd drop either Nalia or Yoshi. Yoshi's a way better thief than Nalia but if you want two mages then drop Yoshi.

I won't say anything more because I'm guessing you're fairly early into the game so my advice is based on your progression up to this point.