Not at all. Incest would be they're both related by blood. He seems to me to have a affection of a surrogacy brother towards her. Definitely not incestuous though.
When you become brother and sister when you are adults, I'd say it's barely incest.Like what if two old people in their 60s gets married. They both have 40 year old children. If those two get together is it sti... QueenChan
It's still awkward tho, but at least you've got less family members to invite to your wedding
the brother is giving something incest