How do I discuss this with my family?

I’ve been wanting a last name change since I was 13. I’ve brought up multiple times with my mom that I would like my last name hyphenated with both her maiden name, and my fathers last name. She said she was okay with it, but she didn’t think it’d be legal, or okay with my father and grandparents.

My biggest dilemma at the moment is discussing this with my grandparents, and father. I haven’t spoken to my father in almost 5 years, which is one of the contributing issues as to why I’d like my last name hyphenated.

Feel free to ask why I’d like it changed, because there are a lot of reasons, but I’m not exactly sure how to discuss this with my family. It’s nothing against my grandparents in any way, I actually love them a lot. But, my father isn’t being a father. And he still hasn’t realized it.

Can you help? How do I do this?

And another thing, is it legal for me to do? Am I allowed to have my name hyphenated if I have both of my parents permission to?