The second question is whether the demon who copulates with the mother or the man whose semen has been taken is the father of the child.

To which Saint Thomas answers, with more or less subtle arguments, that the real father is not the incubus but the man." "For Sinistrari d'Ameno," observed Durtal, "the incubi and succubi are not precisely demons, but animal spirits, intermediate between the demon and the angel, a sort of satyr or faun, such as were revered in the time of paganism, a sort of imp, such as were exorcised in the Middle Ages.
Sinistrari adds that they do not need to pollute a sleeping man, since they possess genitals and are endowed with prolificacy." "Well, there is nothing further," said Gevingey.

"Goerres, so learned, so precise, in his _Mystik_ passes rapidly over this question, even neglects it, and the Church, you know, is completely silent, for the Church does not like to treat this subject and views askance the priest who does occupy himself with it." "I beg your pardon," said Carhaix, always ready to defend the Church.
"The Church has never hesitated to declare itself on this detestable subject.

The existence of succubi and incubi is certified by Saint Augustine, Saint Thomas, Saint Bonaventure, Denys le Chartreux, Pope Innocent VIII, and how many others! The question is resolutely settled for every Catholic.

It also figures in the lives of some of the saints, if I am not mistaken.