I've done the GNR and parkruns in fancy dress, not for charity - just for a bit of fun. The kids watching love it and the support is really good.
I was very aware of trying not to get in anyones way, and made all efforts not to cause an inconvenience at the water stations. To be honest all feedback I got from the other runners was positive, except maybe a couple of folks in the final mile who didn't wanna be beaten by a girl in a ballgown.
Having said that, linking 50 people together is daft, it may break some record, but I'd put money on the fact that there'll be injuries resulting from it on the way round. I did some training in the big pink dress I wore, and it took a good while to get used to the size of the thing.
I've seen the lasses at my local bootcamp trying to run together carrying a length of rope, it almost always ends up with one or two dropping off the end, and the rest crashing together in the middle. I hope the 50 are gonna do at least a few training runs first