IP Office supports four simultanous L2TP/IPSec tunnels.
L2TP does not require a license, IPSec is licensed.
In your case you can do with the IPO tunneling, SCN requires a star configuration.
You will have one IPO connecting to the other four so only four tunnels are needed.
You can always give it a try, if it doesnt work as expected then you can use third party routers.
I would go for the cheapest solution.