Just wanted to wish you luck. Please be honest. Thats the most important thing. I understand how he feels about it being unfair to his other children, but it also might push him that little bit harder to try & find them.
Its unfair for him to put his whole life on hold at the same time. As much as he needs to get in touch with his kids, he does still need to live.
FWIW DH didn't meet his father til he was 19, & while he felt betrayed that his father didn't want to know him, he feels nothing against his father's other children. They aren't as close as brothers & sister yet, but they are mates for now DH actually went out of his way to find them after not seeing or hearing from any of them in 7 years.
I understand all your feelings too.
Good luck to you both xx