ADB uses the work 'should' not 'must', hence although the guidance is that there should one be one bed in each room it is not an absolute measure. I assume it is to cover circumstances where there is a married couple sharing a room, one of whom needs a hospital style bed with side rails, hence a need for two beds.
I just want to pick up on how the word 'should' should (must?) be interpreted. I've said this before on here somewhere. It does not simply indicate that the recommendation can either be adopted or ignored (as in, you should brush your hair before you go out in public (so my wife tells me)). It means that the recommendation should be adopted OR, if not, some other safety feature should be in place that provides an equivalent level of safety.
So the premises in question can have two beds if it can be demonstrated that safety is not compromised by the second bed's presence. Perhaps it's a spare and not used. Perhaps one bed is used by an able bodied carer who will only be an asset in case of fire and not a hindrance. Perhaps it's a couple who simply cannot sleep in the same bed and the twin beds are no worse than an equivalent double bed.
Looking back at the original post I see that the number of beds was unquantified. More than two would be difficult to justify as equivalently as safe as a single bed.