Sorry this happened to your family. I don't know what happened and I wouldn't even speculate. If it were me I would have asked for the manager and told them I had a FP for this ride at this time and why can't I go on it. If that didn't work I would have gone to guest services and lodged a complaint. Especially if I had gotten the FP as part of the paid CL program. Then I would be requesting a refund.
If it was because my FP's changed to multiple experience FP's for some reason I would be very angry also. I wouldn't know they changed because I don't check email or constantly check
MDE while I am in the park.
I hope your brother complained to guest services either at the park or after he came home. This just doesn't sound right to me.