About:GPS for yaw

I read:https://ardupilot.org/plane/docs/common-gps-for-yaw.html

Some questions have arisen:

1: Is pix in RTK state when two f9p points are used? Or do you need a third f9p as a base station?

2: When m8p upgrades 1.40 firmware (1.40 supports mobile base station), can two m8ps be used to complete heading measurement?