Internet Sharing, same LAN
There is no need to use the same network. Usually you can simply populate your DNS-server with the IPs and the names of the hosts in the 192.168.2.0 network.

If you restricted allowed DNS queries to a particular network (i.e 10.0.100.0/24), you have to extend this to the 192.168.2.0/24 net.

In the network settings of the devices in the 192.168.2.0/24 network you have to set up your internal DNS-server as DNS-server.