My ex p had 3 DC when we met, we went on to have 2 ourselves. The relationship with his DC was encouraged by me as he really couldn’t be bothered, I wanted our DC to have a relationship with their half siblings.
My ex was a drug user and was out all the time, home life was crap and he rarely spent time with us as a family. It was quite apparent that his DC were looking for his approval when they did come round, they had no interest in a relationship with my DC, and that’s how it is today, NO relationship.
My DC did nothing ‘wrong’ but the other DC thought we were playing happy families, and excluding them, little did they know (then) he wasn’t a family man with any of his DC.
His DC have a great mum, they’re ok but definitely have issues re their dad. I feel sad they don’t want a relationship with my DC, as they were around in their young lives, I’ve accepted it now (my DC aren’t bothered) but I think it’s the parent in question that causes the issue.
It’s nice that you’d like to nurture a relationship, but I’d leave it b, you’ve done nothing wrong, just an unfortunate position to be in.