Wireless signal is easily "disturbed" by metalwork so presuming these properties are structurally re-enforced concrete then i would say you'd be struggling to get the wireless signal "inside" to the house with standard domestic stuff, even the SMB gear won't provide this power.
If you are able to provide internet to a central point you could then install a 12-port network switch (after the router Cyta provide) and then each of the 12-properties gets a network point hard-wired in them. This point could then be used directly by a laptop, PC, wireless acccess point or another router/switch - you will then have a local area network with the internet connection as a gateway. Downsides are the bandwidth could easily be hogged by one user unless you then install more kit in the middle and also it isn't very secure as each property would be able to "see" the other unless you also control the router in each property. Also if all 12 properties are online together there could be performance issues depending on what they doing with the line. Maybe this has already been quoted on ?
There are "line-of-sight" wireless systems where you could have a central distribution aerial with receiver aerials on each property. There must be line of sight between the devices. I have not seen or used this system personally.
One for Holitec i think ...
(digby - you read my mind
)