We did something completely different.

I am "mummy" and my partner Jeanette is "deddy" NOT daddy
her nickname is "neddy" and my mother in her infinate insanity suggested "deddy" (a combination of daddy and neddy) and it really grew on us - most people get it and the others well .... they are not close enough to cause trouble.
It has really worked for us but we have also had a lot of family support (my family) which has been fantastic.

You've got to do what you feel comfortable with

Belinda and Jeanette