Smart move to adopt TWO kittens! One gets bored by itself, two keep each other amused and less destructive. Besides, two cats are four times as much fun to watch as one cat.
Litter box training a cat is dead-easy! Have the litter box ready and full of litter before you bring the cat home. When you carry the cat into the house for the first time, sit him/her down in the litter box. That's it! Litter box training is done!
The litter box must be kept clean, however. Scooping it once per day, or more often if your nose indicates it's necessary, and changing it entirely at least weekly.
You also need to get a scratching post of some sort. Cheapest thing is to go to Home Depot or Lowes and buy some Sisal rope - the really nasty-feeling scratchy stuff - in about 1/2" or 3/8" diameter. Wind it tightly around a piece of wood - I used a scrap of 1 x 6 that was left over from another project. The cats would rather scratch on that then on anything else (especially your furniture).
DO NOT get them declawed! That is a barbaric practice banned in most of the civilized world (except for the U.S. Declawing is not just trimming their toenails. It's surgically removing the last joint of thier toes at the knuckle! Very painful, and just causes the cat to develop other bad habits, such as biting.