I'd say from 15 months to about 3.5 are the hardest times because they are so very busy... getting into things, asserting their newfound independence, wandering, etc. And you've got TWO in that age range! You do need a break!
My husband travels a lot too and I found that keeping the kids busy and contained kept them out of trouble. We used the baby gates until they were almost 4, then I new that if I was downstairs, so were they. When I moved upstairs, they would come and were always close enough so I knew exactly where they were with little opportunity to get into things they shouldn't be touching. Food was always at the table only (even snacks) and it was confined to a booster chair, so they couldn't get down. The other thing that helped was having a schedule. The mornings we either ran errands or did something fun for the kids, the early afternoon a short show (Baby Einstein or Elmo), nap time, then play dough, coloring, toys, watercolors, etc., dinner, and bedtime routine.
I found that the busier I kept them the less trouble they could get in. And at that age, the solace I found was during the daily nap time, where I could get other things done, or just plop down on the couch. Your older one might be coming out of that routine and when that happened with us I still had them go to their room and have quiet playtime until I came and got them. This was a time to look through books, play with stuffed animals... anything that didn't cause a ruckus. My rule was to stay in the room, play quietly until Mommy comes to get you and if you start hollering to come out, the time gets extended.
So, all-in-all, having a schedule, keeping them busy and sticking to nap time or quiet play time worked well for me. My kids were far enough apart in age that it was a little easier, but I do watch my sister's twins and they are the same age as my youngest (now 4). Having all three from infancy to the present during the day was only bearable by sticking to the above.
Hang in there!