IMO this is totally and completely on the hotel staff -- it is their responsibility to make it clear, with signage/barriers as needed, whether there is one single line (which is how it should be done whenever there's potential disparity in how long each customer takes to be serviced) or separate queues for each position (which is ideal only for quick-processing transactions). In this case, having failed to do that a gentle "excuse me sir, we're keeping a single line if you'd like to get back in your position; we will be with you shortly" would have been appropriate.

The customers in line are responsible for keeping it orderly, paying attention, filling in the resources (yes, if there's an unused checkin kiosk at the airport and you're at the front you must immediately go to it)

I *hate* when it's not clear where a line starts or ends, big gaps or groups of people *near* the line that aren't in it, individual lines that open and close randomly, etc.