<human>: Could you distill the essence of the text into 1-3 sentences?

X-Post from r/birthparents

I've been looking for my biological father for many years, I used a people search and have basic information on him such as his name, date of birth and the last few places he lived, he also has 3 other daughters. All of them are 15-20 years older then me. He is also about 20 years older than my biological mother.

However, all the numbers that were listed for him are out of service. 

A few years ago I was looking up the names of his other daughters on facebook and there was a picture of him in their "family folder" I'm pretty sure it's him. I have photos of him as a younger man when he and my mother were together.

A few months ago, by some bizarre chance of fate one of his daughters came into my work on my day off, but she doesn't know about me. She left her name, number and a photo ID (it's required to enter the business that I work at). I'm positive it's the same person, (they have a unique last name). I DON'T plan on using any of this information from my work to contact her, this just confirmed who she was. I wouldn't want to put my job at risk or make her feel any more uncomfortable then this may already be.

My question is...How do I go about contacting my biological father? The only way I would be able to do it would be through his other daughter via facebook....My mother used to tell me that my half sisters hated her and me and I'm thinking my mother may have been "the other woman."

I no longer speak to my mother so I can't ask for her help and I'm worried that his other daughter may shoot me down if I ask for his information and what not. I don't particularly want to message/go through his other daughter but it seems that may be my only way to contact him. He's already in his 60s and I'd like to meet him and see what kind of person he is before he dies.

Any suggestions on how to approach her or him?
(Sorry if this isn't the proper spot to post this)
<bot>: Need advice how to approach biological father, when all I have is contact info of his other daughter who may not know I exist.