The access between the two different networks is unrelated to DHCP but is related to the IP address and its subnet mask, or related to the routing table.

For example, A & B can access directly. C & D connot if there is not routing table for them.

IP range A 192.168.1.0 255.255.0.0
IP range B 192.168.2.0 255.255.0.0
IP range C 192.168.3.0 255.255.255.0
IP range D 192.168.4.0 255.255.255.0