The older brother's social media posts just scream being in denial to me, the poor kid. I know it's hard to accept that your sister is gone, especially in such a horrible way and with no body as definite proof. However, I doubt ScW would be being charged with her murder unless they had pretty solid evidence he did it even without a body and I would imagine that evidence is being kept under wraps until trial.
I imagine it must be very hard to reconcile what the police are saying vs what your mum (the person you love and grew up depending on) is saying. Our natural tendency is to put our trust in our family and parents. No one can blame BW's family for wanting to believe the best & holding out hope. I think that anyone who might be called as a witness might not find out all the details and evidence until the trial. My opinion only