How can I get a hold of my biological fathers family?

[Lexi Adkins]

Hello I've never met my father nor his family and his family lives in the freaking city as me. My father is no longer in the US but my mother has told me that his family still lives here.(in my city) All I know is his name, and his sisters(my aunts) name and last name. I don't want a father relationship with him because I consider the man that has been with my mom since I was 6 months and who supported me and now pays for my college as my father.
All I want is just to know who they are because after all, I am half of them if that makes sense.
How can I do this? what would the steps be?
Thank you..

ps: I can't ask my mom because she gets upset and is a very stressed person and I really don't want to hear her opinion.. I am an adult, moved out and have a daughter of my own.. this is my choice.