If all the attributes are candidate keys, then any subset of attributes will be a super key
Whatever FD you can form, your LHS will have a subset of attributes
From above stataments, we can say that any FD that can be formed will have LHS as a super-key
This is good enough to say that the relation is in BCNF ...
This is also applicable even after the decomposition of relation irrespective of what common attributes we have (even if there is no common attributes, though lossy decompositions are not recommended)