Without DHCP server present, clients should fall back to APIPA addresses, in 169.254.x.x range.
Since they get 192.168.10.x addresses, this seems more like a rogue dhcp server to me.
When having an 192.168.10.x address, try to figure out where it came from (ipconfig /all , ping gateway , show ARP table to see gateway MAC address, do OUI vender lookup on MAC to see vendor)
