Flying_Fast74
The symptoms you describe are certainly what you would expect from the EDF load exceeding what the battery can deliver.
The simple test would be to disconnect one EDF. If one EDF works normally then try the other EDF individually. It they both work individually then you can be pretty certain either the battery or possibly the wiring/connector is not up to the combined load. A 3000 mAh fully charged 50C battery and in good condition should easily be able to run one EDF at full power for 8 minutes.
Do you have another 3s battery? Even a modest 1800 mAh 20c 3s should be able to run one of those EDFs perfectly well.
Just remember it can save a lot of frustration, particularly with a multi, if you test everything individually on the bench
before you add the components to the airframe.
.