VW Touareg Starting and Power Loss Issues

We have a Volkswagen Touareg, and it's been having some frustrating issues lately. When we try to start the car for the first time, it cranks with a bit of power at first, but then the engine seems to lose strength and fails to start. Usually, it starts fine on the second try.

After driving about 60–70 kilometers, the car starts to feel weak, especially at low speeds. Pressing the gas pedal all the way down doesn't help at first, but then the power suddenly kicks in. From that point on, every time we try to accelerate from a stop, it shows the same lack of power before recovering.

We also noticed that turning on the A/C or using the car’s power outlets seems to make things worse or even trigger the issue. Another thing: we often hear a buzzing or whining sound (like "zzz~") from the rear seat area, which we think is the fuel pump.

The tachometer and speedometer both give inaccurate readings, so we can’t tell exactly what the engine is doing when it happens. Also, the headlights are very dim, even when fully on.

My dad thinks one of the two fuel pumps might not be working, leading to weak fuel delivery, but we’re not 100% sure. That’s why I’m posting here — has anyone experienced something similar or have any ideas what might be causing this?