Dad Re-married A Day Before His Death While He Was Incoherent/unresponsive

This is a doozy.

Our dad died a few weeks ago. Us children were no-contact with him and our mom divorced him years ago, so we weren’t present when he died.

His alleged girlfriend, Rebecca, was at the hospital with him and was overly nice at the end saying she would take care of the expenses and logistics. We let her pay for a few of things because we gave her most of his stuff (car, boat, motorcycle) to sell and pocket the money. We only took a few sentimental things but didn’t want anything from our late father, including any money he had. We are pretty sure he has way more debt/back taxes than savings anyway. He was a drug addict and mostly homeless his entire life.

We finally got around to closing all of his accounts when we contacted his pension plan. We were told that we were NOT beneficiaries and the pension administrator already knew he had died and already said a beneficiary was named. This was our first red flag.

We then looked up and found a marriage certificate to Rebecca for the day before he died. For several days before he died, our dad was unconscious. Our mom went to visit him 3 days before his marriage and said he couldn’t communicate. My sister called him a day before he was married (2 days before he died) and he did not respond to her voice.

We have since gotten a copy of the marriage certificate. The officiant was Rebecca’s friend (they are connected on facebook). One of the witnesses was the officiant’s boyfriend. We spoke to the other witness claims he never signed anything.

We are at a loss for what to do. We are trying to contact hospice to confirm he was unconscious for days before he got married. We also have contacted and recorded conversations with Rebecca and the officiant who all claim he was “in and out of it” but “conscious when he signed the marriage certificate.” Rebecca claims her plan with my dad was to claim the pension money (which only pays out to a spouse, not us children), and then give us the money.

Of course that is pension fraud, and we would have never taken the money. She’s also a drug addict, so I highly doubt she planned to give us anything as she never told us she was married nor that she contacted the pension.

What should we do? Contact the pension funds and give them the relevant evidence so they can investigate/sue? If she married him when he was incapacitated as we think, the pension doesn’t have to pay out to us, so they’d be saving a couple hundred thousand dollars. We also tried to call the cops to report this as fraud but they of course were unhelpful saying it’s a civil matter.

Is she now responsible for all of his debt and back taxes? Should we just stick the debtors and IRS on her?