if you have a good relationship with your ex-sister in laws, now might be the time to turn to them. for me, my grandmother was the only one who wasnt in utter denial about what happened. i never even had to tell her, she just seemed to know, or expect it. . . when she was alive i went to see her whenever i needed to be with someone who wasnt telling me to shut up, its the past, these things happen, and everything else i heard from my mother over the years. i flew there every opportunity i could, and now that shes gone i've lost that rock in my life, that one steady person i could rely on to confirm that i am not a complete loon.
if your mom is set on convincing you that pigs can fly, a little dose of confimation may be just what you need. turn to the people who can give that to you.
in the meantime i'm here if you need a shoulder to cry on or an ear to listen. sending hugs and hope your way.