Yes, Hailie Jade Mathers is Eminem’s only real daughter. Eminem is also the legal father of two other daughters, namely Alaina Marie and Whitney but these two girls are from his ex-partners. He is not the birth father of these two girls.
The name of Eminem started as M&M to showcase the initials of his name, but he became creative and playful and decided to write his name as Eminem. This worked because there are a lot of people who are familiar with him. There are also a lot of people who want to become updated with the various things that he is doing.