Red wire?
Actually there's much more writing about it, than configuring...
RB951 building 1:
create a bridge interface for each vlan
add IP addresses to the bridge interfaces and configure respective DHCP server instances
create VLAN sub-interfaces on the interface towards the SXTAC
add the subinterfaces as ports to their respective bridges
configure a trunk port with vlan subinterfaces to connect a LAN switch for building 1 or configure access ports on the RB951
if needed, set up masquerade for the vlan subnets to the WAN interface, if there is a WAN on this router
RB951 B2:
create a bridge interface for each vlan
create VLAN sub-interfaces on the interface towards the SXTAC
create VLAN sub-interfaces on the interface towards the SXTG
add the subinterfaces as ports to their respective bridges
configure a trunk port with vlan subinterfaces to connect a LAN switch for building 2 or configure access ports on the RB951
RB951 B3:
create a bridge interface for each vlan
create VLAN sub-interfaces on the interface towards the SXTG
add the subinterfaces as ports to their respective bridges
configure a trunk port with vlan subinterfaces to connect a LAN switch for building 3 or configure access ports on the RB951
SXTAC B1 & B2, SXTG B2 & B3
setup the radios to connect, I assume you know how to do it
set the MTU on ether and WLAN interfaces higher than 1500, for example 2000, this is to enable switching packets with the vlan tag