I have a friend who is needing to set up a router with separate SSID that is isolated from his normal network, as they have a granny flat which doesn't have a separate line. 

This is much easier to accomplish with non-mesh setups, but it seems that mesh setups are limited... I saw that Network Orbi's have a guest network option, but it seems they may still pass through multi-cast traffic still, and in some cases, are not even on separate IP ranges. 

Are there good suggestions for a mesh setups for this? It needs to be easily administered by an non-network person, as while I will do the initial setup, I will be handing it over to them to operate.