Will I able to share my internet connection using my MBP's airport if I am connected to the internet through an external USB Wireless adapter?
Yes - Macs have internet sharing where you can use one device to get internet and share it from another.

Most people in a cabin situation set up an AirPort to let all the devices talk and then you would share from the USB to the physical ethernet port. The router would get to the internet from the ethernet and everyone can join the WiFi and share whether or not the USB modem is dialed.

You would set the service order to have the USB modem be the highest connection in the network pane.

What you ask is also possible - just share from USB to WiFi and the Mac will create a wireless network the other devices can join.