can you power a load and charge a battery with a votage source 2x the battery voltage?
The question does not have enough detail to allow anyone to give you a definitive answer. A 6.6V charging source can be a control circuit powered by 6.6V but with sufficient circuitry to allow it to charge a lithium battery properly, or it could be just a 6.6 V power supply - there is a huge difference between the two.

In any case, the issue relates more to how much current is being drawn by each load. You can't just hook up a 6.6 power supply to something expecting 3.3V - it will likely self destruct - and it may take you along with it. If the source can supply 200A and each load requires 100A, then that will work fine, as the current will divide, and allow 100A to flow to each device -assuming it can handle the voltage. Think of it as inflating a tire with 60 PSI, when it is rated for 30 PSI. No matter how big or small the compressor (amps) it will eventually explode your tires.

Good Luck