My Daughter is upset (LONG but important)

So, I got pregnant with my daughter at age 18, had her at 19. I was married to her "father" but he left so many times I went through everything on my own. After her birth he stuck around for a week or so then left me again. It was on and off for awhile. Right before she turned 2 he left and I had enough... told him to not come back. He really LEFT. He was no where to be found. Even child support couldnt find anything on him by searching for his social security number! He was gone for 2 -3 years. Then he finally comes back and has the nerve to take ME to court for withholding visitation. Anyways, we worked it out that visitation would be at his moms every other friday. Then decided that was going okay and let her stay the night every other friday.
THEN about 2 months ago his mom calls and asks if my daughter can go on vacation with them (the ex didnt go) Me and my Hubby, who has taken care of her since before she was 2, decided to let her go. She just got back this past Saturday night and since then said she doesnt want to go next year.
SO, today at lunch she comes up to me and asks ""Is David my real dad?" I asked her why she would ask that and she said that while on vacation her grandma and aunt were telling her that David(my ex) is her real dad and that my Hubby is not.
I explained to her that a Dad is someone that takes care of you and plays with you and is always there for you. Then she said, well, thats my Daddy Mark. I said, hes not "daddy Mark" Hes Daddy.
Now, how should I handle this with the exs family??? I dont appreciate them butting in and causing stress in my 6 year olds life. Or confusing her like that. My Husband has been more a part of her life than my ex has.
Any help would be great!! Thanks!

Tell them that David was not a part of her life so the only daddy she knows is mark and she is going to call him daddy not the other guy. Flat out! They cant tell her who her daddy is and isnt, if Mark has raised her and taken care of you and their son has done nothing then he doesnt deserve to be called daddy. That is JMO though  

I agree. I think they would be acting differently if it was me who left.. u know??

Quoting Babe669:“ I agree. I think they would be acting differently if it was me who left.. u know??”

I'm sure they would. I hate it when familys do this. My parents have custody of my brothers daughter and he acts like its his fault that she calls them momma and daddy and not him. He gets so mad about it.

I just dont understand how a "man" can walk out on his child and then when he decides its easy he comes back and expects everything to be his way. I have raised her, never left, and this is the bullshit I have to deal with. The laws are so pathetic! He should have been found unfit or something!