Since they're so used to pooping in their pullups, it feels like an accident to them if they go in the potty. In a way, this is good news, because it means they already have good bowel control!
So, if you are really ready to ditch those diapers, you have to stage it so that they are likely to have an "accident" in the potty.
Once you know what time of day is most likely for them to have a bowel movement, give them a little juice and a handful of raisins to eat. Then chase them! For whatever reason, at least for my girls, running is the best for loosening those bowels! Don't let them slow down until the potty is in sight. Then drop the pull-up, help them get comfortable on the potty, read them a story, and if it doesn't work, chase them again (a little extra juice might help)! This is a bit sneaky perhaps... but actually quite fun and the brothers might enjoy the process together. As far as I can tell, kids can't actually poop while they are running, so if you keep this cycle up for 30 minutes, it has a good chance of success. If they are tired of reading, a good thing to try is a big bowl full of warm water and bath toys to play with right in front of the potty. The warm water makes them pee -- and sometimes that timing is related to pooping. Only don't try to combine those methods at the same time because the water might be slippery for their running fun!
I drew up a potty chart with the days of the week written on it, and allowed my girls to put a sticker on it for successes (special stickers for poops!).
I also allowed my youngest to put some other stickers directly on the little potty (in a low-splash zone) every time she tried to use the potty. For some reason, she just didn't think the potty was fancy enough, but then she really loved it and wanted to sit on it more once she had personalized it a bit.
Also, if you can stomach it and if you have few rugs, ditch the pull-ups altogether. Kids become emotionally attached to pull-ups. Bring in big-boy pants in full force for them to develop an attachment to. The big-boy pants are for keeping clean, and your boys will get that. Of course, there will be accidents...
When I potty trained my kids when they were turning two, they each had a solid week of accidents almost every day, almost every time. It was a lot of cleaning up on my part, and frustrating. But I felt that I had no choice, since both girls refused to wear diapers as soon as they figured out how to get them off! Then the next week, they were almost perfect, and by the following week, they were dependable potty users.