NTA. I'm normally not for this sort of punishment, but you should take away his phone and any unsupervised computer access. Ground him and send him to a therapist (ideally a female one). Find articles on racism/sexism/slut shamming/etc. and have him read them and then discuss them with you. You have to find where all of this is stemming from and get him to understand why it is wrong, not just parrot out what he thinks you want to hear. It really sounds like he has fallen in with an incel group online.

As for you daughter, you did a good job by standing by her side. You should talk with her and see if her brother has engaged in any other type of abusive behavior or language around her. Make sure that she has a lock on her door to prevent any other intrusions from her brother. Regardless of whether or not she is having sex, he doesn't seem to respect her boundaries.

You probably should have a conversation with your daughter's boyfriend and make sure that he knows that he is welcome at your home. Try to get to know him.

Finally, your parents are kinda awful. You need to tell them that they are being both racist and sexist and that you will not stand for that. You might need to limit unsupervised contact between them and your son for a while. I'd also explain their views to your daughter and tell her that their views are wrong. Let her know that if her grandparents or brother make her uncomfortable that she can talk to you.