you can't see your modem again because it's different class ip.
This is wrong. If you look at the IP Addresses he is using they are in the same IP Class.
GREEN: 192.168.1.4
RED: 192.168.1.5
Router: 192.168.1.1
One of the reasons he cannot see the router is because everything is in the same IP class. When he enters the router IP address into a web browser it will not route out because it will look on green (internal side). If he used a different IP range for his internal network, then he may be able to see the routers web interface.
Suggestion
Green: 172.17.1.1
RED: 192.168.1.5
Router: 192.168.1.1