Any combination of 3 mages/melee level 60-65+ should not have a problem trioing this mission.
The Quadavs are susceptible to both Lullaby and Sleep. 75BRD 75THF 75BLM made incredibly short work of this.
As for doing these missions even though your not on them; everyone in pt receives same xp (my parties average attempts bringing 380xp), Allied Notes are awarded after talking to OP mission giver in town.
Reports indicate that a large battalion of beastmen raiders has been dispatched to Ruhotz Silver-mines. Travel to the mines via the Rolanberry Fields (S) and aid the legionnaires stationed there in defending the location.