I have setup my TP Link Archer VR2800 router with two networks:

1. a local network, where all devices can talk to each other, and
2. a guest network (which I connect IoT devices), where I deliberately restrict devices from talking to the local network

The router acts as a DHCP server.

I have a DNS server that is on the local network (this is Pi-Hole). I have hard coded the router to DHCP announce the IP address of my local DNS server (rather than use the default DNS details of my ISP).

While devices connected to the local network can access the local DNS server, devices connected to the guest network are unable to access the local DNS server - because I have disabled their LAN access. 

Is there a way I can have both local and guest networks access the local DNS server but NOT let devices on the guest network access the local network? Alternatively, am I able to offer a DHCP server which announces one set of DNS details to devices connected on the local network (i.e. the local devices use the IP address of my local DNS server for their DNS) and a different set of DNS details to devices connected to the guest network (i.e. guests use the IP address supplied by my ISP for their DNS)?

Thanks