In my view, the most urgent ...

In my view, the most urgent issue that need to be addressed is the pH (5) of the water if it is being drunk as it is. The drinking water with this pH level can be extremely harmful for the health. It can eat away human body in the similar way it is damaging the pipes. Therefore, pH needs to be raised immediately. A combination of lime, soda or soda ash should work well. Secondly, the well water should be analyzed to see if it falls within the WHO guidelines at least. If not, it should be treated to remove the undesired constituents. Thirdly, I assume the iron pipeline should have been internally lined or coated and raising pH should stop further damage. Anyways, damaged portions will have to be replaced. In case, most of the pipeline is rusted and leaking, it would be wise to replace the it with corrosion resistant material such as PVC or HDPE. However, make sure the material can sustain the network pressure.