I'll echo what others have said--it is completely reasonable to have them share. We have two who are 16mo apart, and they started sharing when the younger was consistently sleeping through the night (DD was 20mo, DS was 4mo).
Just know that it usually means when one wakes up for the day, they will probably both be awake. During the night, they do fine sleeping through the other kid's noise, but if it's close to when they would be awake anyway, one tends to wake up the other. We've gotten used to it, and we'll be adding a third to the craziness in that room eventually...but there are still days (at least once a week) where I wish they could be in separate rooms during their nap. If your kids tend to sleep for the same amount of times at naps, it should work out fine...otherwise, it can mean dealing with a little extra grumpiness in the afternoon because someone got woken up before they were really ready.