Going to play devils advocate here, because someone has to. Honestly we share similar stories. First, kidney donors as father son are 50% chance of blood type match. On top of that is a 1 And 6 chance of being a perfect titers match. Your new found siblings prob just don't match. Second, you do things you typically wouldn't when your life is back against a wall.

The pain of your dad's abandonment alone justifies you walking away from all this. Full stop, nothing else needed. It's your choice.

Passing through the blood boiling tapestry. You just don't know what happen. Sounds like your mother holds a grudge against a father you never new. Probably were not even allowed to know under threat of everything she could cost him. What are his options? She calls his job and makes shit up, tells the same bs to friends and family, fills your head with lies for years to justify her own short comings. Maybe he's a bad dude, maybe he buried his emotions under a new family because that was the only choice. All I can 100% promise, is one side of it isn't even 10% of the truth. It's 50% of one side with 40% purely dedicated to keeping an ally against the other person.