Are you saying that 6 - 8 engineers can keep a fleet of two (civvie) helicopters airworthy 24/7??
There are actually 22 helicopters in the contract, one spare for each type. Each unit will have two of which one is the standbye. The second will be available for scheduled maintenance but on a 4 mans hours servicing to 1 hour's flying this will be very infrequent. When a major servicing event comes up then the spare will fill in. The spare will also normally be available to proceed to an outstation if there is a protracted heavy workload.
It is normal in the civilian world for a helicopter to be detached for long periods with just the crew and two engineers.