Well, I don't know what villa-1 and villa-2 are but here is what you can do:
- using Zentyal as DHCP server, such design will need 2 different NIC, one for each network
- with static IP management, you can do almost whatever you want but you will need either to add virtual IP to Zentyal or adapt your netmask.
My feeling is that your question is not related to Zentyal features but rather basic network design. How to have 2 networks communicating ?
Will Zentyal be used as router
between these 2 network ?
I also don't understand your point about DNS
So in this network I just give dns server by zentyal server's IP
Sure you can do this. Assuming routing is OK, Defining Zentyal as DNS for any of your network is always feasible and is not impacted by your domain (whatever meaning you have here) is. You may have to define network domain is Zentyal DNS, that's it
Instead of design, I would suggest that you rather describe what you intend to achieve in term of feature:
- file sharing across these 2 networks ?
- transparent routing ?
- network isolation ?
- shared DNS content ?
- something else ?