my chins often try to use the same dust bath. My one cage has 3 girls. I let two take a bath at one time since i have two dust bath houses. Even tho i put out both houses they often try to hop into the same one. I have heard stories about chins getting stuck or hurt doing that tho, so i dont let them.
They are very anxious to get there sand bath so by the time i put one in, they are both trying to get in. After the first one gets in i cover the opening with my hand while i reach for the second house. Then guide the second chin into that house; making sure they are both in a separate house. Usually after that they are good.
Some times mine are so anxious to get in that one will hop into the sand bath house before i have fully laid it down. And that adds some weight to it, so the house hits the ground a good bit harder (or louder as the case might be) and then that sound will scare the heck outa them and send them into a panic lol.