Im in no way suggesting that your W has made all this up. Why does your W feel the need to talk to you about this? I think calling the OMs FIL is a bad idea. 1. you dont really know what is going on and could create more problems for everyone involved. 2. The last person they prob want to hear from is you or your W. They are taking care of their daughter. Ultimately, she is the only one they care about. Not you, or her H or your W.
You CAN NOT control what your W does. You need to stay out of this drama. It's very sad that the OMW attempted suicide. She needs help and it sounds like HER family is taking care of that. I think you will cause more problems for her. The last thing she needs is the affair being thrown into her face again. Leave it alone. That may sound callous but she is being cared for.
Now YOU need to take care of YOURSELF. Stop letting your W drag you into her drama. Because , im sorry, but that's exactly what she is doing. Have you been GALing? Staying upbeat and detached when your W is around? If you have and this is her attempt to get a reaction from you. Bad news, but she won this round. STOP REACTING. If you havent, she is STILL WINNING. So Stop it.
If I sound unfeeling and mean Im sorry for that. I sympathize with the OMW and her family. If you feel you need to support her, do so in your own heart and mind. Not publicly.