In 1962, there were allegations that Marx fathered a son, Freddy, out of wedlock by his housekeeper, Helene Demuth, but the claim is disputed for lack of documented evidence.
Not agreeing with marxism here, but what you’re saying is just ad hominem. Marx could be a horrible person to his daughters and wife and still propose correct theory on economics. There are far more credible criticisms of his work.