1 -- Juv Red Knot -- the fine black subterminal band inside a white terminal band on the scapulars and wing coverts is just about diagnostic for the species and age (and, BTW, visible on the upper bird in the second photo of #3).
2 -- Juv White-rumped -- dark legs, no webbing, pale base to the bill
3 -- Juv Pectoral in first pic
4 -- Semis
5 -- Semi/Western -- White-rumped is notably larger than Semi and its wing tips extend beyond the tail tip (all features presented in field guides)
6 -- Dunlins
7 -- Semis/Westerns