but they didn’t abandon him

They lied to him, went behind his back and then treated him with “he’s our dad”. If that’s all it takes to be their dad then he shouldn’t have gone 50/50. To me, what they did was simply worse than cold ghosting and abandoning.

his emotions like a grown up

Because grown ups are supposed to be perfectly capable of managing all deep emotions such as shame, fear of abandonment and jealousy? Also funny how they aren’t grown ups at 19year olds. When do they get to start taking responsibility for their actions?

Getting to know your BIO parents behind your parents back, when it’s a sensitive topic to them is betrayal. He drew the line there and they shat on it.

Again, if they knew it’s a sensitive topic for their dad they could have talked it out. They are adults as well, when are they going to learn how to communicate? Judging by the “we’re coming to Christmas” they are entitled assholes who will never learn how to communicate and her mother and your mentality is further enabling that. They fucked around and found out.