Inbound and outbound are conceptually unrelated, so solve one, then the other.
For your inbound, you can set up an “any/any” Inbound Route to handle the start and end range for your DIDs. Anything that comes in one one of your trunks will process through the Inbound Route and, if the DID matches (which it will because it is an “any/any” route), you call will to to the destination specified by the Inbound Route.
I assume you have a router of some kind provided by TATA. If that’s the case, you set up your FreePBX box so that the Ethernet Address on eth0 to 10.0.71.90 and set the Trunk so that it points the “host” to 10.0.71.94. The network will be set up as 10.0.81.88/255.255.255.252.
There is going to be an issue when it comes time to set up phones, since 10.0.x.x is a ‘non-routable’ address, so your “external” address will be messed up, but this is a start. If you can get this set up to talk to your ITSP, you should be able to get started.