I agreeDon't invite Hector. Make it absolutely clear to you Mom that you do not want Hector at the party,and that if he is there, you won't be.
Lt her know exactly why, and stress that you are not prepared to tolerate his behviour to yourself and are not willing to be associated with an event where he will subject your friends and relatives to the same kind of sexual harassment (use that term, if your mom or others try to persaude you to let him come)
Explain that you are happy for Hortense to be there and are content to let you mom make the call as to whether Hortense is invited alone, or not invited, or whether mom speaks to her privately to say that she is welcome is she comes alone.
I am also in the camp where it would affect my view of friend, if I were subjected to sexual harassment at their event, and learned that they knew that the pepetrator was likely to behave in that way. I wouldn't necessarily end a friendship over it, but it would affect how I thought of that person, and how much I felt able to trust them and trust their judgement in future.