[Mockingbird]

It may have less to do with caring about sharing medical information than it does with the acknowledgement that your are his child and the part that he played in your mother's situation years ago. His wife may want that left buried, as that may cause her insecurities because she would have to deal with the fact that her husband has a child with another woman (from his past) and that may rekindle feelings. She may be worrying that you or your mother may make demands on his time and/or finances.

Anyway, just considering other possibile reasons why they wouldn't share the information. Your dad may be in some shock and need some time to process things; hopefully he will acknowledge you and give you not only what you are asking for, but also what you need and want. If not, maybe you could go to paternal grandparents?