Does anyone know how to deal with Paranoia/OCD/Whatever the hell this is

What do your parents think about the situation, btw?

My father has been completely shut out of the picture, my grandmother thinks he's out to poison the family. My mom is very glad when gran does this kind of thing because, in mom's own words, 'a break at last, she finally is bothering someone else'.

Now gran is going on about 'I wanted to return the keys to you! But I couldn't, because it was very dangerous! They might put things in your mother's makeup and make her look like a monster if she puts it on!'
I think she is also trying to humiliate me into giving in to her demands, because she's demanded that my access keys to the fridge (it's in a locked room) and toilet be taken away, and is talking about buying a pot because she clearly can't let me have access to the bathroom since my keys are so easily compromised now with an unlocked door.