Stephane...good luck with your launch!
Sometimes two bilge pumps are mounted side by side of redundancy (extra safety) in case one fails. Also sometimes the FLOAT switches which turn them on are mounted at different levels in the bilge...one low and one high for extra help in a real flood. You might look for the float switches to see if that is the case.
The thing that is puzzling to me is that they are in your head. They should be in the bottom of your bilge unless they are simply shower sump pumps.
No longer posting. Reach me by PM!