Reddit, My dad is going to marry a woman he barely knows, and we've heard some bad things about her. What can I do?

Now before you go telling me I should be happy for him and he's a grown man and all those other cozy things, I just want you to know this is a serious situation that I can not take so lightly. My parents are divorced, and I don't care if they date/marry anyone else, but this is one of the worst situations that could have arisen out of it. I'll start from the beginning.

Now, what you need to know about my dad is that he's a Jehovah's Witness, and kind of an irrational person when it comes to things like this. He believes this woman was "sent by God" for him, and is jumping into it way too quickly. I wouldn't mind him dating/marrying another Jehovah's witness because they are generally nice people and it wouldn't be unorthodox for him to find comfort in another person in their group. Fine.

But this person JUST joined them (im thinking just to get to him), and has now, after maybe a couple months of regular dating, has gotten him to propose, and they are getting married in February. The early engagement isnt the worst of it, or the fact that she has two kids and no regular job yet, its the fact that im already hearing terrible things about her.

For one, where I am, (where she used to live) I asked around about her out of curiosity because I knew nothing about her. Ive only heard bad things such as:

1. Got fired from her job for being too hot-headed. (Bossing people around and being too negative.)
2. She used to work with a guy who was a known CON ARTIST who later went to jail for it.
3. She's been in and out of jobs for the past few years, and hasn't really settled down anywhere.

These are just a few that put me at unease. Next thing I hear is that she wants to live in the US. How does one get a visa fast? Marry a citizen. Usually i'm not this paranoid but there are enough red flags. His mother and sisters have already tried to warn him but he isn't listening.

What can I do to make my dad understand that he's doing this the wrong way? To make him at least take his time to get to know this person before he goes and makes a mistake?

TL;DR:Dad is rashly marrying a woman who is potentially using him, and I don't know how to stop him. Help?