ozplane
As FIS is technically a non-radar service it doesn't matter if you all wear the same squawk. Most military units now have a 'FIS' squawk (have a look at the SSR allocation plan in the UK AIP). The reason for it is just to 'tag' you as traffic working that unit. Should you be working that unit and require a RIS or RAS you'll find you will be issued a different squawk unique to you while you work that unit.