You can basically use any ADSL router or a normal router with the single port ADSL router.
Both solutions will work. I have not seen any ADSL router in stock here at the dealers though so you might have to get both. If you already have single port ADSL router for the mtnl you can put that in bridge mode and connect it to any 4 port router and from there you can give connections to the individual pcs.
Login info and port forwarding will be through the 2nd router.