Innsbruck - Valencia is about 780NM IFR distance. The C414 with vortex generators has about 1000kg useful load. This means with 8 POB, it can't carry much fuel.
If they were planning to go to Valencia non stop, then they must have exceeded the MTOW.
I don't think there is enough information out there to say whether an engine failed or whether it was a CFIT. In one report I read they were doing this trip VFR which sounds odd with that kind of aircraft and mission.