silkspin, congratulations to your husband on his sobriety and standing by you on this.
How I would probably handle it would be to go over there with my husband and say directly to him, "last night when you made a pass at me, it made me feel.... (sick, nauseous, angry, etc.). It's completely not okay and being drunk doesn't make it excusable." Yes, with your sister present.
Putting a light directly on problems is necessary. State facts.
What could make things better from here? Counseling for him, for all of you? When drinking is involved, it could be best to take that out of your lives for a time and with self-work, see how things go.
If you can push for your BIL to get counseling right now, that would be great. As with recovery of anyone, look at your BIL's actions, not his words. After such a huge thing like this, his actions need to be just as huge towards getting therapy and serious help, if he truly wants to help to heal this with all of you. It sounds like maybe he has a drinking problem and/or other issues going on. Try to look beyond the immediate problem to giving some kind of solution. Whether he agrees, whether your sister believes you, that is up to them. Stay true to yourself.
The only person you can really do anything for is yourself, so that's where I'd be heading -- self-work. Have you ever had individual counseling? ((((hugs)))
Can you cancel the vacation, or can they or you and your husband go with other friends?