Hi Brandon,
Correct me if I'm wrong but, as I understand it, if one of these tenants has a fire in the middle of the night they will have to get themselves and their family to the front door, open it and then, with the possibility of smoke or even flames around them, remember a code to be able to open the grill to further their excape.
That doesn't sound ideal to me. It's a bit like something I've come across a few times where people dead lock their front door at night and then put the key away in, say, a kitchen drawer. It doesn't make for rapid egress.
But if the grills could be opened by turning or pushing a handle (and these can be shrouded against external operation) then I couldn't see a problem. Or, maybe simpler, ensure that the code is indelibly written on the back of the front door.
The point you make about fire service access is a very common one. If the fire service can get in easily, so too can less trustworthy people. I haven't ridden on a truck for a few years but I believe most carry small angle grinders that they can use to remove the grill. I would be inclined to approach the local fire station and see if they carry these and ask them to be aware that they may have to use them at your building. Then they're pre-warned to take them with them when they first enter the building on arrival.
Stu