You can get battery load testers and check each battery
Vident iBT200 9V-36V Battery Tester Car Battery Analyzer
100A 6/12v Battery Load Tester
Some examples, hard to troubleshoot with out tools.
IMO only way to know for sure condition of each battery check disconnect each battery and load test it individually to weed out the weak or dead cell batteries. I would also take close look at terminal connections? Now if all batteries charge up and check good you can rule them out and start looking for why there drain so quickly?