Search Results: how to ask a stranger out

I met my father three times in my life, last time I saw him I was about 12 and he just dropped off the radar. Never took an interest in me or paid child support. He is a complete stranger to me.
Last year I took an ancestry DNA test and found two half siblings I never knew i had through my father. One is still coming to terms that I am her sister (we haven't spoken since Jan), the other sister I met in person and we are getting to know each other.
She has had some contact with our father sporadically over the last twenty years (she was adopted at birth and found him as an adult). Through her I have found out a lot of stuff about his family and his life. He is a convicted criminal, has a drug problem and apparently was/is obscenely wealthy.

My sister has hinted that we should ambush/confront him (as he never told her about me) together.
On one side, I would like to ask him questions about the family, namely if there are more siblings and about the grandparents. He is also getting older and people die, plus his lifestyle is rough. This sister has also had a falling out with him, so she may not be able get any more info about the family from him. On the other side, I really don't know if I want to waste my time on a piece of shit that could suddenly fuck up the life I have worked tirelessly to build.

So I am kind of unsure what to do. What would you do if you were me?

Now a days it seems there is a tremendous demand for stranger chat, video chat etc. Most of top 10 grossing apps in play store are of chat catagory.. at least in my country. Can anyone help me understand why do guys forget friends and ask strangers for friendship! Isn't it weird? What do you think?