There may only be two books in the series, one is a regular novel and the other is a choose-your-own-adventure type gamebook. I read them in 1997 so I assume they were written in the 90s, 80s or even 70s. I found them in my school's library on the same shelf as The Adventures of Goldhawk but I don't recall them being illustrated.
The regular novel was a fantasy story about a warrior meeting a young sorceress while travelling, and they began travelling together.
The gamebook was set after the regular novel and was about the warrior, sorceress and I think two other characters fighting their way through a castle or tower. I recall it being quite long for a gamebook compared to the Goldhawk series.