Living with never knowing what really happened (trigger warning: sexual misconduct)

I started to work through this for the first time last week, with my free coaching session (thank you Madeline!). Still processing and would love more coaching on this:

Below is my circumstance and model. I am looking for coaching on my thinking to help me and my family move forward.

C: 2 months ago, a fisherman called 911 and reported overhearing from 2 nearby kayaks my adult brother-in-law say to my 11 year old daughter “Have you ever had sex with a boy? Have you ever been naked with a boy?”
Brother-in-law and daughter both deny this happened.

T: I don’t know who to believe, my husband and I will never know the truth
I don’t know how to support my daughter when she is saying nothing happened
I don’t know how to protect my 3 daughters from this person going forward
I don’t know how to proceed with relationship with brother-in-law and sister-in-law or how to “be” at future family gatherings

F: Confusion, despair, concern/worry

A: Not committing to attending a family gathering this week where I will see brother-in-law for first time since this incident.
Not responding to sister-in-law’s texts
Avoidance of moving forward with relationship with brother- and sister-in-law

R: Tension in family, I am unable to support my daughter because I don’t know what really happened.
I am contributing to my mother-in-law’s despair that her “family will never be the same again” (I know this is her own model, but I still feel like my actions are making a contribution to this).

I understand this model needs to be broken into several models, but trying to summarize it all here.