First one is correct but its only connector and other is only wires no connectors and need to attach it yourself.
This is correct one with cable 6in and 2 female 2pin connectors.
https://www.sparkfun.com/products/8535I was under the impression that up to 16 boards can be on one cable so if you need more than 2 boards you have to custom make your cable.
Yes that is correct. The ready cable is good only for 2 boards without possibility to add another board.
So you should buy one long cable + the same number of connectors as you have boards. It should be easy to install the connectors, just snap the cable in and connector will strip the insulation off.