Chillphil, how do you know the other two engines will start ?
Appears to be no quick fix, just two much data and questions need to be sorted.
Maint checks required after flight through Ash, expect some very long turn arounds !
Another point of interest, although some data of aircraft and Ash is known, it's possible that newer aircraft/systems/engines will not be the same as older types.
Not operating aircrafts in these present conditions in the short term may be a far cheaper option in the med/longer term.
Safe flying to all.