Chartering a bare-boat and taking it through multiple countries would be very ambitious. Most charter companies want you to stay in the same island country that they are located with some exceptions as in the US & B.V.I.'s and maybe St Martin/St Barths. At most they allow only travel to an adjacent island country such as SVG / Grenada. But traversing a dozen countries from B.V.I.'s to Grenada would be challenging as you are not the owner of the vessel and you are operating in a "commercial" charter regime. That's got to be complicated at best. Generally when a charter boat gets a half dozen countries away from home base, the officials start thinking maybe the boat is stolen.
So wouldn't it make more sense to do multiple charter rentals, one after the other, as you work your way down the islands. It is easy to hop from island to island on SVG Airlines or other small island airlines. Then you don't have to worry about returning the boat back up island again. With only two months allotted weather windows could suck up all your time and you would be "trapped" somewhere and not be able to get the boat back on time.