I have a telecom Italia router with ip 192.168.1.1 and 2 mikrotiks connected trough eth1-wan to the Telecom router. the mikrotik-1 have 192.168.1.10 on the eth1-wan interface and the mikrotik-2 have 192.168.1.20 on the eth1-wan interface. then all the other ports are bridged with assigned networks 192.168.10.0/24 for mikrotik-1 and 192.168.20.0/24 for mikrotik-2.
-- I am assuming that you have a default route (default gateway) as the Italia Telecom router, probably something like 0.0.0.0/0 ====> 192.168.1.1
-- Therefore if you are connected to the Italia Telecom Router, you can connect to both Mikrotiks, since they are all on the same subnet of 192.168.1.0/24
-- But if you are connected to either of the Mikrotiks, you cannot connect to the other, because you must route from 192.168.10.0 to 192.168.20.0 and vice versa.
-- You need to add static routes on each Mikrotik to the other mikrotik subnet. For example, on Mikrotik with address in range 192.168.10.0, add a route that routes all traffic to the 192.168.20.0 network to the gateway of 192.168.1.20. On the Mikrotik with address 192.168.20.0, add a route that routes all traffic to 192.168.10.0 to gateway 192.168.1.10
EDIT: mkx said it better than me, we must have been typing at exactly the same time ...