My main concern is how the dynamic would work (like why your dad never told you. Or if he didn't turn did he die like Ashs mom?)
If you can give me the dynamic I'm ok with it (though bare in mind demon lineage is eternal since they live forever so you probably have ancestors that are alive born in ancient Rome. and the same with Ash)
I would say he did not tell me because he never wanted Eric to be a demon and wanted him to die. Simply because he saw the boy as a disappointment and did not want to have a demonic son like him. And maybe even have him come and approach Eric and Ash (after they finish with the transformation) and try to mess things up. Or he could some how know Mabel and try to kill her and the boys.
But he just did not tell him because he wanted to watch him die from afar, his father never wanted a son. Also another reason Eric and his father have no relationship.
I would say that he was disappointed that he had a child at all, and from the signs of him being ill from a young age, that he would have a demon son. More responsibility on the father but he was content with watching the biggest mistake of his demonic life die slowly from a distance.
I should note that any child of a demon would be a demon. But still if he was a guy that doesn't like to be tied down it makes sense that he would not want a son at all. Especially since demons don't die he would be stuck with one forever.