Best Friend - Dance?

My name is Linda, my fiances name is Evan. I`m going to be 21 on our wedding day, right now I`m 20, Evan`s 21, he`s six months older then me.
We started dating at 16 and both our fam.`s are very supportive on us going to marry.
We just have a "few" problems with the planning of the wedding.
Evan is the oldest of three, he has a 12 year old sister and a 19 year old brother, his parents are happily married.
We have no problems with his family.
The problem is my family.

My mother got pregnant with me at the age of 15. My father broke up with her. My mother was living in Italian at the time. Her family was very christian and strict about having to marry the father of the child.
My mother keept me.
My mother moved to the US when I was 3. When I was 5 she married my stepfather. I call my mother by her first name because she felt to young to be called mom or mama but I call him dad. My biological father never showed interest in me, my mother has his adress and so has he hers.
The father/daughter dance will for sure go to my "dad".
Any suggestions on the song? i want a song that shows our special relationsship.
And I want to do something for my mother,too. I can`t dance with her but....I want to thank her for everything she did for me.
And then there is my best friend. We`ve been friends since pre school. He means the world to me.
I thought about dancing with him. I asked Evan if that would be ok with him and what he thought and he said if it makes me happy I should go for it.
So I need a second "special song".
Julius was the brother I never had, I am an only child.
Any advise?
How should we handle the stepfather-thing on the invitations? He is my dad. Not my bio-father.
And there is one thing left:
Evan wants to dance a special dance with his little sister. He was 9 when she was born, he was like her second dad. Any advise on what song to pick for the two?