Aussie, I only caught up with this today, I feel for you unfortunately your son can see sex in his future and his hormones are making all his decisions. Unfortunately the people we fancy at 19 are not always the people we fancy at 25. You have done all you can for now and things will be more complicated once he is married espeacilly if his wife objects to visiting his Df'd father. He may well be destined to make his own mistakes but these may be what he needs to break free. Remember there is no armageddon and no imminent destruction so this will play out.
Your daughter seems to have a mind of her own good for her. IT may be that she makes a bid for freedom earlier and that she already knows enough to make an informed choice. The fact that your wife is being stricter with her than her brother may also make her more likely to rebel. Keep doing what you do they will wake up eventually and they will have somewhere to go and someone to support them lucky them.