MSP432+BLE+ Debugger interfacing
Q1

The most simple method: after the firmware for the BLE-µC is created, convert the binary data to C-Array. Include this C-Array into your MSP432-firmware. Now you can transfer the BLE-firmware easily, as it is available as static resource.

The only limitation is the amount of storage available on your MSP-µC, it's firmware and the BLE-firmware both need to fit on the MSP433 flash.

Q2

By looking at the technical reference manual of your BLE-µC. The firmware-upgrade procedure is not very complex and Atmel's manuals are sufficiently detailed.

Q3


  If I don't connect the serial pins of debugger to MSP432 how can I see
  the serial data on terminal in PC?.


You will need to find another interface to connect to your computer. UART is not a bus: you cannot connect more than 2 devices over the same wiring.
Maybe your MSP432 has another set of UART-pins that you can use?

Or you could use Bluetooth, you just happen to have a BLE device in your design anyway.

Another possibility would be to pipe the UART-data over the SWD-connection of your debugger. This would at least work during development.