2000 Mercedes Benz S500 Water pump failure

I've taken my Mercedes to the dealership n had a diagnostic ran on it an received the list my brother is a fine mechanic an told me he can fix it so I purchased a water pimp from napa an he installed it perfectly fine I drove it for maybe 10 miles an it started to squeak an started to over heat so I shut down letting it cool. Brought it back to my brother an had him take it off an took it back, installed the new one we took it for a test drive around the block an it sis it again so we got another water pump thinking it could be a faulty water pump again so napa had one sent from Germany itself my brother installed it while thinking it could be a relay switch I purchased one of those. Car performed great drove it down to southern Oregon a 5 hour drive an everything was fine I get the car back and drive it for maybe 5 miles an my dash says dead battery please service so I pull over and my belt has broken I notice sum melted stuff on my water pump as if something got hot an tried to spin my water pump by hand an was froze up. This is my 3rd water pump that has gone out an can't seem to figure out what is causing it to fail. If you have any idea what this could be please let me know what your thought is on this car.