Set up different DNS servers for different networks

I'm configuring my EdgeRouter Lite to have four networks

1. VPN
2. ISP
3. DMZ
4. GUEST

For the DNS, I have it set to Forwarding. However, I don't want to have the DNS requests for the VPN connection going out through the ISP connection.

Would it be best for the forwarding to be disabled and to set the different DNS servers on the DHCP configuration as DNS 2? 

The configuration for the DNS Forwarding

		forwarding {
			cache-size 150
			listen-on eth1
			listen-on eth2
			listen-on eth1.10
			listen-on eth2.10
			system
		}

For the DHCP

	dhcp-server {
		disabled false
		hostfile-update enable
		use-dnsmasq disable
		shared-network-name VPN {
			authorative enable
			description "Connection through VPN"
			subnet 172.27.1.0/27 {
				default-router 172.27.1.1
				dns-server 172.27.1.1
				domain-name vpn.domain.net
				lease 3600
				start 172.27.1.10 {
					stop 172.27.1.25
				}
			}
		}
		shared-network-name ISP {
			authorative enable
			description "Connection through ISP"
			subnet 172.27.2.0/27 {
				default-router 172.27.2.1
				dns-server 172.27.2.1
				domain-name isp.domain.net
				lease 3600
				start 172.27.2.10 {
					stop 172.27.2.25
				}
			}
		}
		shared-network-name DMZ {
			authorative enable
			description "DMZ Network"
			subnet 172.27.3.0/27 {
				default-router 172.27.3.1
				dns-server 172.27.3.1
				domain-name dmz.domain.net
				lease 21600
				start 172.27.3.20 {
					stop 172.27.3.25
				}
			}
		}
		shared-network-name Guest {
			authorative enable
			description "Guest Network"
			subnet 172.27.4.0/27 {
				default-router 172.27.4.1
				dns-server 172.27.4.1
				domain-name guest.domain.net
				lease 3600
				start 172.27.4.2 {
					stop 172.27.4.25
				}
			}
		}
	}