I have a mikrotik for a while now and replaced 2 older switches with mikrotiks now.

However :

My older main switch sits directly behind the modem.
It's "internet" ip = it's "lan ip" and this works just well.

With the new boxes setting the lan ip = local ip i lose everything.
It only works if they have theyre own subnet.

So sorry for the nooby question but :

How do I properly setup the 2 additional mikrotiks to have each theyre own that is accessible from above and below and keep the whole network within the same range? Still allowing vlan and vpn setup with the old main switch as gateway and dhcp.

Not sure I fully understand but maybe if you

1) Bridge the ethernet ports
2) Assign the IP to the bridge, not the ports

Is this what you want?

Thing is I want port 8 to run over vpn aswel.