The best tool to use when working on stuck nipples is patience.
First of all, a nipple wrench is very unlikely to solve the problem alone, attached to a drill or anything else. The vast majority of them are far too soft and the nipple will just damage the shoulders of the wrench. There are hardened nipple wrenches available for a few dollars, and the 'investment' is worth it in the long run. So, first, buy one ot those hardened wrenches.
Second, some sort of chemical intervention is needed. The corrosion in the nipple threads will be almost impossible to overcome (the nipples are bonded to the cylinder at the molecular level) without help. There are many such products and several 'urban legend' fluids that will provide some help in this area. You'll probably get lots of suggestions about diesel fuel, transmission fluid, WD-40, etc. I've used them all have no advice as to which is better for what - it depends on the level, type and amount of corrosion and we have no way of knowing what that's like in this case. Get a good commercial rust removal product and use it as directed.
Except, again, remember patience. Set the cylinder on it's face and fill each nipple recess with the anti-rust fluid of choice. The order the nipple wrench. Leave the cylinder sit until the wrench arrives. Add some fluid every day until that happens. Then turn the cylinder over and put some fluid in each chamber, so that it can attack the corrosion from the other side.
After about 3 or 4 days of adding the anti-rust fluid you are ready to start trying the wrench. Steady, even pressure. If that does not work, go back to the fluid for a couple more days and then try again. If there's still no success after a few attempts, use a propane torch to heat each nipple - it won't take much heat.
If none of that works, buy the cylinder.