I think these would be better of in the English Slang forum, do idioms count as slang?
To guild the lily means to try to improve something that is already good, or that can't be made any better: "You look beautiful like that, you are just trying to guild the lily."
A dog in the manger is like a Scrooge, someone who has something and doesn't use it, or doesn't need it, but won't give it to others either: "He is like a don in the manger. He is not going to eat that, but won't let me have it".
No idea about the other 2