Cisco WAN :: 861 Enabling All Internal Devices To Be Reachable Through NAT

I need to connect 10 branches to a datacenter using cisco 861 routers because the ethernet sollution the provider gave us can't assign more than 32 MAC addresses for whe whole network. So we have all our servers at the datacenter with a central firewall/router and all remote branches with a static route to this router. We would like to make all branches local networks available through NAT or another better solution so network devices at the datacenter network can communicate with all local devices accross all the brances.
 
I've tried to set up a dynamic NAT from outside to inside the network and didn't work, set up static ip routes for both datancenter and remote branchs and also didn't work. I just would like to make the routers work in a transparent way, no blocking of anything, passing all traffic in and out the network.