Separation anxiety, but only when in the same household?

Hello, I read the wiki but this is a very specific question and situation. So my boyfriends parents and I both got puppies. They are 5 months old and grew up together. Since my boyfriend is home from work during the day, I drop my pup off at night on the days before I work the next day so he can care for them both until they are old enough to be left alone while we are at work.

We are trying to get them used to being kennelled separately since one day they will no longer be together every day. But 2 nights in a row now, since trying to kennel them separately, they get anxiety and mess in their kennels. They are let out regularly overnight to potty and can hold it just fine when they are in their individual households.

However, when they know they are in the same house as each other, it causes anxiety and they stress and mess in their kennels and we don’t know what to do. They are completely fine over the weekend when they are not in the same house.

Any advice or any products that have a high success rate for this anxiety? I have read the wiki, but the problem is exactly that they dont have separation anxiety in seperate households while being kennelled, but if they are separated in the same house, they are anxious and make a mess unless they are together in the same kennel.