Are my eggs dud?

[therenter]

So dd3 told our head teacher that we were going to get chickens at which point he said not to buy any as he wanted to get in some rare breed eggs and hatch them at school.
Headteacher got in Maran bantams and they have been in an incubator in school
Hatch day was yesterday but nothing happened so today after school we bought the eggs home. I float tested them after checking for pipping of course. 5 sank small end down to the bottom. The last one floated at the top with the tiniest bit sticking out of the water but no bobbing about.
I am thinking they are all dud's - have put them back in the incubator for now but am really not expecting them to hatch.
what do you think? And should I be concerned about exploding eggs!