It's so simple...
- Windows Server must have two network adapters (for Local network and for Internet /NAT/);
- Every Client PC in the Local network should be in the same network group (LAN);
To have Internet and to share it with the other PC in the local network - must have 2 (two) network adapters;
1) Adapter 1 (NAT): NAT stands for Network Address Translation. It's a way to map multiple local private addresses to a public one before transferring the information.
2) Adapter 2 (Local Network): It should be set to "Internal Network" The network name "intnet" it is important to indicate that they are on the same network:
Client machines only need 1 (one) network adapter with "Internal Network" setting with name "intnet".