So making it multiple choice definitely made this one a bit easier. Fall shorebirds can definitely be tricky - just like fall warblers. But tricky just means fun. Also, you tend to see a lot more shorebirds in the fall as they lazily make their way south as opposed to the spring where they want to get north to get done what needs to get done (bow chicka wow wow).
So here we go then:
1. Dunlin - this non breeding bird may not look anything like the color seen in a breeding bird - but the thick, long, drooping bill should be enough to give it away. Overall it is a grayish brownish bird (usually a little more brownish tinge to the chest than the back).
2. Semipalmated Plover - I suppose you could argue that I cannot eliminate Common Ringed Plover from this picture. In which case I could go into some more detail. But for the basic part here there really is no other shorebird that has that chocolatey brown back and the little white around its neck. You can see another one in the blurry background of the photo that matches up exactly.
3. White-rumped Sandpiper - This bird is obviously a little bigger than the other two around it. Its wings are longer and it has a white superilicum. It is also more brightly patterned than the birds near it and the breast is not nearly as dingy as you would expect with a SESA.
4 & 5. Semipalmated Sandpiper - The back on these birds is much more uniform and scaley. There really is no rufous to the upperside (as opposed to Western). The cap is dark. The bill is relatively short and straight (longer and slightly drooped for Western)