I am usually not a reactive person, certainly not with strangers. However, I came across your post and remembered you as the same grandmother who raised concerns about the amount of activities your grandchild participated in.
I have no opinions whatsoever on children sleeping in the same room. I do, conversely, have an opinion about in-laws who offer too much input on how there grown children are raising there own children.
If you are posting on these boards simply to commiserate, and then keeping your findings to yourself, that is well and fine and I commend you for seeking an outlet outside of your family to do so. These boards, after all, are a place to find opinions and comfort from a group of people going through similar things as you. However, I sense a tone of meddling underneath your post. If you are in fact planning on going back to your daughter-in-law and saying something like, "Well the other mommies on Mama source said...," that is perhaps the fastest way too ruin your relationship with you daughter-in-law, and in turn your son and grandchildren.
My own mother-in-law is overbearing, and the more she pushes toward us, the more I pull away. That is human nature. It is the fight or flight reflex. I know you must love your grandchildren very much (as well as your son and his wife, I assume). So the last thing you want is for your daughter-in-law to have to choose between fighting with you or fleeing from you.
So, give your son and daughter-in-law some space. They are the ONLY people who should make decisions about where their children sleep. And really, the only opinions they should have in mind when they make such decisions are those of their own children.