That is pretty rude...on the up side at least they contacted you saying they would be late. If this had been planned, and then you reminded them a few days ago, then I would be upset. If you just reminded them the day of the brunch, then I would have to put some of the blame on you. If you are always on time for things, then being late to a function will drive you crazy. Maybe they all need a wake up call...text them back, say brunch cannot wait that long and they will have to get together another time. But if you do something like this, then be prepared for one of them to rebel and note if you are a minute late to anything.