You might want to stagger their bedtimes, the 2 year old say at 7:00 and the 4 year old and 7:40. My kids 4 and 7 share a room and it was a hard time when it was still light out and I put them to bed at the same time. Total pain, so I stagger their bedtimes, which makes my 7 year old get special time with me, my younger one is fast asleep and it saves me so much stress.
They have programmed themselves to wake up, being consistent no matter how tired you are and put them back. Also warning them sternly they are not to wake each other up and HAVE to stay put! Do it over a weekend so there isn't work or school being effected by the lack of sleep! :) Right now they are running the show and will continue to do this as it is a habit now.
Put up a chart and challenge them both to whomever can stay in their own beds each night the most will get a prize, do a sticker or whatever and at the end of a month (they both can win or tie if both do it) have a reward for whomever did it.
My kids love challenges.