some of my boyfriends friends call me yenge, is there some name i should call them in reply?

Yenge
1. uncle´s wife, affinal aunt.
2. sister-in-law, brother´s wife.
3. used when referring informally to one´s own wife or to a friend´s wife: Yenge hanım nasıl? How´s your wife? Maalesef yengen gelemedi. Unfortunately my wife couldn´t come.
4. woman who helps and attends a bride.

So generally speaking, it's the way your boyfriend's friends call you as their friend's girlfriend (I'd rather prefer to be called by my name though!!!)

yeah i know what it means and apparently its not an offensive term, i think its more geared towards the brother's wife/sister-in-law meaning of it.

if they call you "yenge" (sister-in-law), you could call them "enişte" (brother-in-law).

There isn't anything you can call them in response to their 'yenge'. This term is often used as an informal & honorific way of referring to a close relative's or friend's wife or girlfriend. Although eniste would be the male form of yenge, it is not really used in that way. In certain ways 'yenge' may sound a bit like peasent speech, it is very commonly used, and is not vulgar or offensive. However, you may consider asking them to call you by your name. Yenge is often reserved for older ladies who do not qualify to be called 'abla' due to age difference. Or, it is used as a slang.

e.g. Yengen olur...
Maca gidersek yenge bozulmasin... / Would the 'yenge' be annoyed/pissed if we go to the game...

My grandmother's sister's son, who happens to be an 'amca' to me, is married to an English lady, whom I have been calling Angela Yenge since I was a little boy. I would have called her Angela Abla had there not been an age difference.

In other cases, if there is no age difference, then, yenge is simply being used as an honorific in the sense that they consider you to be their friend's partner, and respect that (meaning they wouldn't hit on you out of respect).

I have to say that I find the idea of calling people amca, yenge, yigen, dayi etc a bit superficial and irritating.

If they are calling you yenge, then, I am assuming that you are on a first name basis with them. Otherwise, it would be a bit inappropriate to call someone yenge immediately after you meet them.