Watchguard Licensing - two M200s, two locations - do I need two licenses?

Out of 40 remote sites, two biggest sites have M200 fireboxes each (one site runs a pair as a failover, so technically we have three fireboxes). Feature Keys are due to expire so need renewal soon. I'm just browsing for prices and I wonder if I actually need two licenses or just one? That's a "Total Security Suite" I'm talking about.