Family Issues Support Group
Family issues is a huge range that go from minor conflict to major misbehaviour and even abuse on the part of individual members of the family occur. Whether you feel you are in a dysfunctional family or you're dealing with a very specific issue, this is the place to talk about it and find others who might be going through the same thing.

Can you ask him to blow his nose rather then sniff because its better to get the gunk out then stay in his system,
Knocking, I'd tell the daughter and the boyfriend that when he comes over you'd ask that he respect your wishes and KNOCK on the front door please.
If he is there all the time then well, money for food would be nice too, because you are now feeding another person and that is not cheap.
Does this 'prince' come over when she is not there? If yes, then tell him to go home as you've things you need to do and don't wish him in your house alone.
I doubt very much that you can say anything to make her see the light on this guy. Could you ask a close friend to speak to her about him? Someone she may respect the advice from.
Best of luck to you and I hope his mooching ways soon turns her off.