Just a shot in the dark
If you can use the things you are asking about, look in the company Ops Manuals. If they do exist that is where they will be, if not there, you can't do them..........period.
No alternate airfield = Island reserves and to the best of my knowledge is 2 hrs normal cruise speed hold, then splash down. Regardless of the number of engines.
Again, if it is not in the company manuals, forget it, forget ICAO. Your local CAA (JAA ops or not) will grant.