A lot of complexity in that setup. Why do you need the two slates in router mode as opposed to AP mode? It sounds like you’ve got at least three separate physical subnets

If you put everything in one network with a default gateway, DNS server and DHCP server handled by the mesh router, and then hung the slates as APs, printers, switches, NAS and computers with networked drives all off that network, you would save yourself a lot of aggravation.