Some of my other favorites are Worm Loves Worm and And Tango Makes Three. They should all be on Amazon!
There's a book about a Prince... can't remember the title though. :S
(It might be called, "The Prince")
Edit -It's called King and King Tons of great recommendations at the bottom.
As to your Third question - I don't know that it is all that important to be honest. I think we, as adults, tend to focus on issues that children will naturally take in as normal. It has been my experience that they don't have any questions about it and when asked they don't seem to care about much more than their own personal issues. However, if you run into a child with a lot of questions or concerns like "why did Billy hit me and say my mommies were going to go to hell?" then colorful picture books help confirm to them that your family is perfectly normal and it is Billy that is wrong.