<human>: Can you give me the gist of the text in a nutshell?

(Quick intro, first post ever, been browsing for a bit now and decided to ask for help on this)
This is a pretty quick story. My father was known to jump from woman to woman, my parents met young, mother kept me and decided to raise me away from him due to several very valid reasons. I saw him once a year for a long time but knew very little about him. At 22 I moved in with him and got to know him more and more, we've been really having a good time having each other in our lives. Then one night while he's very drunk sits me down and informs me I have two older sisters who live in England! He only stayed in touch with one of the mothers (Two girls from two different mothers) the mother would send him an update every year up until she was around my age. Last he heard she had graduated from the University and is happily married.
I have a name, I've had this name for a year and have done nothing with it. How do I do this? She probably thinks someone else is her real father, is it my place to completely mess up her life? I decided when I found out that I wouldn't chase this, worried about shocking this poor woman, but the more I think about it the more I wonder if she knows about me and if I should try. According to my father the other mother knows all about me.

Side note: No one knows about this, this is just between my father and me. It's made things very awkward when my grandma coddles about me being her "First grand daughter". Womp-Womp.

Also I live in the US making this even more challenging.
<bot>: I have secret sisters and don't know if I should find out who they are and how I should go about it.