DS has his father's surname. DS result of one night stand with a friend, had to beg to get him on the birth certificate let alone use his surname. My surname was the same as my abusive father's and I wanted DS to have a link with his bio father since he wasn't sure if he wanted to be involved in DS's life. I was 20, would make different decisions now.
DS1's father is around and involved. I met DH when DS was very small, we have DD1 and DD2. DS calls DH daddy, knows his father is his bio father (calls him by his first name), but DH is the father he has always known. I changed my surname to my mother's maiden name when I was 22 and DDs had that as their surname at birth. At the time I asked DS's father about changing DS's surname to my new surname, he said maybe, I didn't do anything about it as DH and I got engaged.
Last year DH and I got married. We have now changed DDs surnames (and I have changed mine). We want to change DS's surname to be double-barrelled, his bio father's surname and then ours, but his bio father is refusing permission (we need his permission to do it).
He can't really offer any explanation which makes sense to me: he says DS can change his name when he is 'old enough to make the decision' (DS is 9 and very clear he wants the same surname as his sisters and parents, especially now DD1 is starting at the same school). He says his parents will be upset.
AIBU to want DS to have my surname as well as his bio father's?