The older generation has this custom. Daughter and son-in-law can't sleep in the same bed in their parents-in-law's house. However, it's different now. Your parents moved to a new home, so the place where your parents used to live is no longer their home. Your parents' family should move to a new home first. Therefore, the original home is no longer their home, because there is no home. Of course, some parents-in-law have no taboos in this respect. If your parents haven't moved in first, you still can't sleep together. Personally, I suggest you move your parents' home to your parents' new house first. It doesn't matter if you don't have a home first. You can sleep together.