That transformer is unsuitable for use at 25 Hz, as it says 150 kHz.

It's a flyback transformer, and no flyback transformer is suitable for use at 25 Hz, as they are meant for frequencies far above the mains frequencies, like tens to few hundred kilohertz.

The auxiliary winding is to power up the mains side switch mode chip that drives the primary coil.

It reallly has two parallel primaries, and three parallel secondaries, and as the datasheet says, they must be paralleled, it is not for adjusting the turns ratio.

That transformer is unsuitable for use at 25 Hz, as it says 150 kHz.

It's a flyback transformer, and no flyback transformer is suitable for use at 25 Hz, as they are meant for frequencies far above the mains frequencies, like tens to few hundred kilohertz.

The auxiliary winding is to power up the mains side switch mode chip that drives the primary coil.

It reallly has two parallel primaries, and three parallel secondaries, and as the datasheet says, they must be paralleled, it is not for adjusting the turns ratio.

And it really has three separate windings on the same core, it does not matter where exactly they are drawn, but the aux is meant to be used on primary side so it is drawn there. The secondary has typically better isolation than aux so it is drawn alone on the other side.

The primary to aux ratio really is 2.8 to 1 and the primary to secondary really is 2.33 to 1.