There is a diagram in FCOM chapter 34 ( ADIRS ) which shows what air data is provided to what computer.
In general the air data from CAPT, FO and STBY probes is processed by an air data module ( ADM ) to "computerise" it before passing to each ADIRU. However the ISIS receives raw data directly from the probes ( not via a ADM or ADIRU ). So if all ADR's are inoperative the ISIS will still provide basic information.
One method to identify a faulty ADR is just to compare ADR 1 ( CAPT PFD ) , ADR 2 ( FO PFD ) or on the EFIS switching panel select ( AIR DATA SWITCH ) CAPT 3 ( now ADR 3 is displayed on CAPT PFD ). If it's not obvious then set a know power and thrust from the QRH and this should result in a know IAS. This should determine which ADR's are showing valid information.