From when I worked as a census enumerator in '91, it goes on whether you have your own, separate 'house number' and mailbox.
So if you all live at, say, 32 Acacia Avenue, you all have a matching front door key and a shared kitchen, then it'll be one form.
However, if your bedsits are numbered something like 32A, 32B etc., and you have separate facilities and mailboxes, as you would in a purpose built block of flats, then you should have separate forms.
If in doubt, check out the FAQs on the census website:
http://help.census.go...help-and-information/