create bridge that has all vtnet's, virtual machines' NICs

ifconfig bridge create
ifconfig bridge0 name vnat0

network would be 10.0.0.0/24

ifconfig vnat0 10.0.0.1 netmask 255.255.255.0

set IP on bridge, that would be gateway in virtual network,
server DHCP with dnsmasq on that bridge to give IPs to VMs

with PF create NAT routing