Damaged radiators are never easy to repair, even by professionals. The results can be patchy and quite often lead to more leaks later, or worse, blockages.
Lime deposits are also difficult to remove and reduce the efficiency of the radiator markedly.
Sometimes the best option is simply to renew the radiator/s, and although expensive is a lot less than the damage caused by an overheating engine.
Alternatives you may wish to consider: