Connecting 3 systems through WIFI modem

Hi guys,
Really sorry if there is another thread like this, but I have nowhere else to turn.

I've got 3 computers at home- 1 is my laptop, one my brothers laptop and 1 desktop which my parents use. We installed an MTNL broadband connection(Modem DNA-A212) 6 months ago at which time only my laptop was in the house. So the WiFi internet connection works fine in my own laptop. But when my brother came and the folks bought the new desktop(with WiFi) some weeks back, I found that both the computers have to use a LAN cable to connect to the internet i.e. the WiFi connection is not working for them. Sometimes it gets connected but then the connectivity is "Local Only". There is no problem at all with the connection in my own laptop using WiFi. Can't connect my Nokia 5800 phone nor my brothers X6 using the modem either which means basically, only my laptop is the one that can use the WiFi to connect to the internet!


I tried using the IP addresses, subnet masks, etc which is written in my laptop with their systems but nothing works with WiFi. Is there something I'm missing? Any help is appreciated and if there are also other threads that help, please give links.