Control px2.1 cube with bluetooth through I2C

Hi everyone, I need some help please

Im new in this, I have a PX2 cube for a new project, and my goal is to create a mission in AUTO mode but when I get to certain WP the Quad has to wait for a signal that comes from a bluethoot to stop holding position and height, and rang to the next WP when it receives another sign of this. The connection in principle is through the I2C port.

I have seen that the TBS crosfire communicates with Pixhawk through Bluethoot and I2C, so I conclude that communication via mavlink is possible.

My question is how should I do to get this? I thought that the moment the Quad arrives at the given location I could send the Mavlink command to enter Brake mode, and when I have to continue to the next WP I simply remove the Brake mode, but I have not found how to do it; So the next thing that has occurred to me is that I send the command to move to Loiter mode maintaining height and position, but I find the problem that I have to tell him how long he has to be in that mode and that is not my goal, a Solution would be to give a longer time than necessary and when you have to continue remove the Loiter mode and go to Auto mode, but do not know if it will continue to the next point or start the mission from the beginning.

I would very much appreciate someone telling me if my approach is correct or not from my absolute ignorance.

And if it were not, if someone were so kind to show me what to do or where to look for a solution I would be very grateful.

Thanks in advance