I have setup my Archer VR 2800 with a local network and a guest network. 

I know there is a way that I can toggle on/off access of guests to my local network in the router settings. However, I would like to know if there is a way I can restrict guests from accessing my local network other than one IP address on my local network (the reason is this one IP address on my local network is a local DNS server I have configured with Pi Hole). 

I effectively want one device on my network (in addition to the router) to effectively sit above the local network and guest network and be accessible to all devices connected to the local network and guest network. Other than this one device, I want to isolate devices on the guest network from those on the local network. 

Is this at all possible?

Thanks in advance