Dentures, if dropped even a short distance like...in the sink, can break. Postal people THROW packages. I've seen it many times. Heck the FED-X guy stood out on my sidewalk & tossed a box 10 foot to my front door! Good thing it wasn't glass. Anyway wrap them well in bubble wrap, insure them & make sure you get delivery conformation.
I had 13 teeth upper pulled at one time. I had "immediate dentures" put in while I was still under. I was told NOT to take them out. Had a dental visit the next day. Dentist took them out & had me rinse. He checked for sores/bleeding/etc & back in they went. I even had stitches. Every dentist & situation is different tho. Hope your brother makes out OK.