Welcome to the Wefugees community.
Unfortunately we don't have experts for the Turkish (marriage) law in our community (afaik). However, we had a question about the same topic here on the platform in the past. Have you checked out the answer provided in this thread yet? It says that in principle it should be possible to marry even if your fiancé is residing in Turkey illegally:
In general, I would suggest to get in touch with Turkish officials. They will be able to give the most precise advice on how to proceed and the requirements to marry. As far as I found out both of you need to submit the following documents at registry office (Turkish: Belediye):
- a valid passport/ID
- a certificate of birth
- a certificate of no impediment (to prove that you are eligible to marry)
- if you've been married before: a certificate of divorce or a certificate of death of the previous spouse
- (sometimes) a certificate of health issued by a local Turkish health authoritiy
- and 4 passport pictures by each spouse
If you don't speak Turkish you will need a translator that is present at the ceremony.
To make sure that your marriage is acknowledged worldwide you should ask Turkish officials to issue a certificate of marriage (Turkish: Evlenme Kayıt Örnegi).
I hope this answer is helpful to you. That's all I could find out so far.