How do I get my mom to understand I need to bring my own items and have some privacy when I move in with her and dad?

Even if one's parents had a lot of money, it would have been difficult for them to leave a non-elder friendly house where the mortgage was paid, and move into a retirement facility where they would need to pay rent and HOA fees every month.

And speaking of not wanting to use their own money, I use to have to run my parents all over hill and dale for appointments, shopping, CPA, haircuts, you name it, and take time off work to do so, plus use their car which I disliked driving with a passion.... it use to irritate me to no end because my parents could have afford to hire someone to drive them :P So much resentment on that part because I developed major panic attacks while driving during all those years, and to this day because of that my driving range is just one or two miles.

A live-in interloper. Does that make sense to anyone? Stay where you are. Let them make other arrangements.

Not sure if people remember my laments from 2 years ago when I sold my condo, put my things in storage and moved into my childhood home. BAD IDEA! I had zero privacy, was treated like I was a kid again (where are you going, who is calling you so late --after 8pm mind you -- what time are you coming home, etc). I was miserable! Ashlynn is wrong, however, you can get your life back--I did! After 6 months of feeling I was a captive in a small bedroom with no privacy, alone time, I moved into a small 1 bdroom apt nearby. Ahhhh...I can eat when I want, get phone calls at 10pm or later if I want, sleep in, sit on my own couch. Yeah, I had to buy furniture again but it was so worth my sanity! My mother was controlling, always has been. But now, I can leave after a visit. I'm not her captive anymore. When she starts in and gets on my nerves, its "see ya" and off I can go to my own place, my own tv and my own bed. Do not make this mistake! I am 1 mile away from them. Find a small place like I did and be near but not living with her. Good luck

Fortunately the sister-in-law with dementia after surgery for a brain tumor refused to live with anybody; and we knew that moving her would push her over the edge.
The thing we had to remember is that she could NOT learn anything--her ability to make new memory was gone. There was not a whole lot anybody could do except to get a home care person to get her meals and generally keep things up as well as possible. She fell once, and was found by a neighbor; but wound up back home after she rehab. Her daughter took her in but she kept trying to leave and walk home (60 miles). I will admit she was one of the very few people that I would lose patience with; she would keep asking the same impossible thing over and over and over...the key was that nothing got through to her. Finally she was found in her home by her daughter one morning. As frustrating as it was, it was merciful that she was finally at peace.
Sometimes people do change for the better if they reach a point where they forget their most annoying behaviors, but just remember that people with memory issues do not learn, so the odds are that they will not change their attitudes.