Old boiler/water tanks

[thebullettrain]

I'm currently buying a 1950s house. However, it has an old boiler in the garage, a water tank in the loft and some water tank (of some descript) in the main bedroom. I've come across the loft water tank and boiler before but the concept of the third cylinder. Does anyone know what that Is about?

I had a quote to have them pulled out and replaced with a combi boiler and the builder sad around £4,000 including changing the pipes but excluding the new boiler purchase.

I'd like to know, please:

what is the two tank and one boiler concept?

Once I replace it would it be best to replace all the pipes or just pump some solution in the boiler to clean the pipes?

Is the quote pretty reflective?

The old boiler flute contains asbestos , is some special treatment required when removing it?

Thanks PHers! I've tapped this up on my iPhone so excuse any typos.