K.E.
I don't have advice on training twins - I actually came to this post to read the responses! But, I can help a little as far as rewards. Go to a teacher's store or a craft store where they have scrap booking supplies and buy a sheet of little stickers. They are usually very cheap for a couple hundred sparkly stars or smiley faces etc. I may have even seen them at Staples. Make a special chart for each boy and for every time they are successful, they get a sticker. 1 sticker for getting to the potty in time, a sticker for pulling pants back on unassisted, a sticker for remembering to wash hands, and so on. Cottonelle used to have potty training kits free - they include a story book, a sticker chart, stickers, (the chart and stickers are for kids who are into the process a bit), and a cardboard guide to hang from the toilet paper holder to show how much toilet paper to use. Try www.cottonelle.com
Another reward I would use in conjunction with the stickers - after 1 full line of stickers my kids would get to watch one extra video that day (TV is a privilege in my house). We've also done trips to the park, bubbles in the bathtub, exclusive time with mommy, go to the dollar store to pick a toy, etc.
Best of luck,
K.