Homeostasis in Families

After class on Tuesday, I started thinking about how my parents went about dealing with me and my sisters all being in college and out of the house. Both my sisters are older than me and were away for college years before I left, but my first year I was gone, my parents were happy to see us out of the house and have it back to themselves. However, after my first semester went by, my mom became very sad seeing everyone home for the holidays and leaving again so suddenly. She started calling me twice a day and was always telling me i should come home over the weekends to visit and get a home cooked meal. I didn't think too much of it, just that she wanted to see us some more, but then my dad got involved and would go behind her and tell me no matter how much she asked, I needed to stay back in Lincoln so she could get used to the fact that we were all grown up. His plan didn't quite work however.
The next year my oldest sister graduated from college and got engaged. She didn't have a place to stay so for 9 months before she was married and moved to another state, so she stayed at home with my parents while she worked and saved up money for the wedding. My mom was so happy cause she had one of her children back home.
The following year, which is now this school year, my dad was hoping we would all be out of the house again but my middle sister got accepted into Creighton Law School and to save herself some money, decided to live at home with my parents. My mom was yet again ecstatic to have another child home for the school year, while my dad was a little mad that we kept going back home. My sister is now looking for an apartment for the summer and the next school year to give my parents their time alone again but my mom is still trying to persuade her that it would be best if she just stayed at home, mostly because it's "cheaper" than an apartment. I now know why she is having such a hard time letting us go, even though this should have happened a long time ago.