Hello,
first of all. A VLAN acts as if you have dedicated switch for this lan. So if you setup a vlan and putt all the comera’s ports on the vlan (lets call it 2) to untagged only this cameras can talk to each other.
You need to add a vlan on the pfsense to the LAN Interfache. It will lock like lan.2. This port needs to be setup to tansport the vlan 2 tagged. On the pfsense you need to assign the new “created” interface for vlan 2 and give it a name and a ip. Like 192.168.2.254.
Then you should be able to see the new interface lan.2 unter services / dhsp server and can enable it.
I sugged you start wie a port on your switch attach a pc to it and check if you get dhcp offers.
If you camera’s are poe then you can powercyle them via the switch and could leave the ladder where it is stored 
Hope this helps if you have questions feel free to ask.
Best Regards.