The main airport is Istanbul (IST) on the European side, however, Sabiha Gokcen (SAW) is also an option for the Asian side and lots of European flights land here. You can select the airport based on which side you are staying on

Remember, the wedding is on the Asian side, but it does not have a lot of nearby hotel options. If you want to arrive a few days earlier to do some touristy things, European side (Karakoy or Besiktas) will be a better option. But then again, the traffic in Istanbul is always bad. You MUST plan at least an hour and a half travel time to the venue. Please plan accordingly, we don't want you to miss the ceremony