Well done to Iwan and John for correctly getting the 6th species!
Here are what I found. Did I miss any?
Probably the hardest to identify are the Red Knots. A better photo in less harsh light might show that they have a grey rump, but this feature isn’t much use in strong overhead tropical light. Instead, I find the broad white tips to the inner primary coverts, contrasting with the rather dark outer wing (primaries) is the most useful feature – at least on photos!.
Thanks to all participants!