I was curious to hear other people's advice on this:

So I'd like to start dating this girl, but I found out that one of her best friends is my ex's sister in-law.

As long as it doesn't bother either of you.

So, what difference does that make?
Will you guys see each other on a regular basis?

I have questions for you? What do you do for a living? Do you have a Job, education, etc? What are you gaining dating women? Is this friends with benefits, Taylor Swifting it, or are you actually serious about being in a relationship that could lead to being a husband with children?