Help! One dead bantam...why?

[JJA]

Any ideas? I had trusted my family to look after my five bantams (various breeds) whilst I was working last week 8am-8pm. Mistake! Found one dead this morning, an empty food trough and dirty water. They had also not been cleaned out for about four weeks and I found lots of red mite. I have treated the hutch, dusted the chickens and given them food and water. Their behaviour is different - they are much tamer than usual, happy to be handled. They are staying very still and quiet, with beaks slightly apart and since eating have started doing a funny twitch kind thing (a bit like gulping, forcing their heads and necks forwards as though struggling to swallow.)
Any ideas anyone???

 

[JJA]

Update... One looking a bit better and has taken herself off to bed. The other three still looking odd and not looking like they'll make it through the night.

 

[farmer boy]

Update... One looking a bit better and has taken herself off to bed. The other three still looking odd and not looking like they'll make it through the night.

are they walking around slow and stuff ?? if they are feel their throat to see if its hard if it is stroke the throat for a while with each one if not they will choke and die but thats only if their throat is fool of food