Edward,
Costco only sells boneless butts (unfortunately). So, you have two 6 lb butts. They will not smoke like a larger bone-in Boston butt (sorry). It would be good, if you had some butcher's twine to tie them up, but since you don't, don't sweat it. Coat them in yellow mustard, and rub, and into the smoker they go. I'd smoke them at 235, until they hit 190 internal temp. Be sure to use a water pan, on the floor against the smoke box.
I would allow 2 hours/lb, so you're looking at around a 12 hour smoke. Butts, under 7 lbs, tend to take longer, and so do boneless. You have a bit of a "double-whammy" with this one...smaller butt, and boneless!
Endure to persevere! Trust your probe to give you internal temp, and let it go (door unopened) until 190. Take out, double-wrap in HD foil, and place in a cooler (ice chest), covered with towels, for at least an hour. Should be great!
Pork butts are very forgiving....lots of internal fat, and hard to mess up!