If you are trying to Drop in are you trying to Drop in on your household devices or someone outside of your household? Within your household just say the name of the device that you want to drop in on. For instance: Dropping in from Bedroom Show to Kitchen Show. Say Alexa Drop in on Kitchen. However, if you are trying to Drop in on someone else's household you cannot at the current moment specify which device you can drop in on. Now if you are close to this person what you can do, is ask them to make the device you want to drop in on the Default. They can do this by changing the Permissions on that device to ON. While setting the rest of the devices in that house to ONLY MY HOUSEHOLD. Now only the Device in that person's house that is set to ON will receive a drop in call from someone outside of that house. You can do the same in your household if you only want a specific device to receive Drop in Calls. I have written Amazon about changing this so that someone from outside of a person's household can Drop in on any device by just stating which device to Drop in on. I would suggest you do the same if this is what you want.
I am trying to do video calling. All three Alexa Show's are in different locations. One is at my daughters dorm, one at my husbands office, and one at home.
Are they all associated to the same Amazon Account? If so use Drop In not calling. Think of it like this it would be impossible for you to call yourself from your own phone. It is the same with the Echo Shows. If you have them associated with the same Amazon account it would be like calling yourself. So instead use the Drop In feature. You can just specify when Dropping in. For example you can say: Alexa Drop in on Amanda's Dorm or Alexa Drop in on Hubby's Office. However you have those devices named that is how you will Drop In.