With boneless butts, I always tied them up. You will see when they are finished that they easily fall apart, so the string helps to keep them in tact until you are ready to pull. As for doing two, the time allowance would still be 2 hours/lb for either butt, not added together. If you have a 9lb and a 10lb butt, then allow 20 hours (10lbx2) and you will be more than fine. The #2 might hold both butts on separate racks, and you would still only want to use 5-6oz of wood.