Device settings issue

With a laptop connected to the network you can open a terminal/console interface and get an idea about the other devices it is aware of. If you have the console open and issue the command ping 192.168.12.255 that sends ICMP packets to the broadcast address of the LAN and all clients will see those. Your client should get responses and then you can issue the command, "arp -a" which will list the ARP entries in the clients ARP table. There will be a listing of different IP addresses and each client's hardware address. Each IP address is of course a different client recorded in the table. If they are alive and active they should respond to the pings and then the client that issued  the ping to the broadcast address should provide the listing. If the count of devices is as expected to the number you have well there you go. You know they are there and respond.