What I do in LXC is to have the server interface being a bridge, so the server has IP1 set on the bridge, and the four container interfaces becomes part of that bridge. Just configure your container networking to be:
lxc.network.type = veth
lxc.network.flags = up
lxc.network.link = <your server bridge interface>
lxc.network.name = eth0
And then you set your container IP as usual in the container. You can also set the IP in the lxc config if you want:
lxc.network.ipv4 = <IP>/24
lxc.network.ipv4.gateway = <gw IP>
How you do that is up to you. There are also other network types, so please do read up on that.