BQ24040: operate with BQ51050

Hi TI,

Now our customer use BQ51050+BQ24040 as the connection below.

Here are the question:

1. Why back-to-back MOSFET(CSD75207W15)?

2. is it possible that current goes from battery side through BQ24040 to AC input?

3. Can we use single PMOS?

Thank you.