I'm so sorry about this anon, really I am. Blogpost incoming:
My father was like this and, up until recently, I had to put up with it until I had enough. We went from a large house to smaller and smaller places when he refused to keep a steady job, yet refused to get rid of anything. My mom was too worn down from being, and hiding the fact that she was, emotionally abused to do much about it, and my brother has a temper of 0 to fistfight REAL quick, despite being the nicest dude you'd ever meet, so it was up to me. The 'conversations' were like talking to a crazy person - always in circles, always word salads, and ALWAYS everyone else's fault but his. When my brother wanted to get a new/larger bed, he wanted to donate the twin sized one he had since we were kids, (he's about 6'3", so it was long over due). The second we put it outside my dad had a complete meltdown - saying it was 'his' because he bought it 25 years ago, that we should have told him first, etc., despite us saying it was going to charity/tax write off/etc. My father never wanted to listen to me because he had this unspoken mentality of 'women folk don't know better', (something he hid well until he didn't), so eventually when I went to grad school I packed up my things, my brother, and my mom, and left him to rot in his own squalor.
Now, I'm not saying your parents are anything like this, since mine is an extreme example, but you honestly have two choices here. 1)Tell them how uncomfortable/claustrophobic the conditions are making you and how you'd like to put a lock on your door for privacy, (or similar conversations) or 2)Figure out if a dorm/apartment life is available. I hate to probably repeat what's already been said to you, but it is 'their house', especially if you're not paying rent. It's a hard truth that you can't make them change if they don't want to listen. I wish you the best of luck, however, and just know that, someday, you won't have to live like that anymore.