1. a) We don't know what they look like. b) What BP said
2. There was a good theory, inspired or borrowed from the Momotaro story, about Peach's origin somewhere in the Mariology thread.
3. Not official, but I read that her name might be Claudia. Other than that, we have no knowledge whatsoever about the mother. For all we know, the Koopalings might not even have a mother.
4. a) He's a member of the royal Koopa family, so yes, he and his offspring are gonna be slightly different from other Koopas. b) What better way for a Koopa King to take over the Mushroom Kingdom than by marrying its princess? But, also, in the Paper Mario continuity, Bowser has the hots for Peach.
5. a) Who said they're related? b) What BP said