Toxic sibling/ parents

Guys I don’t know what to do here

I have a twin sister and over the past few years she’s just been getting crazier and crazier

Not that long ago she texted me saying she took her dog outside and someone with red hair was sitting in her car and by the time she walked over to them the person was gone

Another time she snapchatted me saying there was clowns on her ceiling and then sent me this pic

Other times she will ask me to drive to the town she lives in to bring her something as simple as a drink or food even though she lives 30 min away from me and most of the time I can’t because I’m at work or soon have to go to work.

She will then blow up at me and belittle me saying I’m selfish and never do anything for her or my family and that I’m a terrible person.... ALL BECAUSE I WONT GET HER MCDONALDS

and then when I thought she couldn’t get any crazier.... she asked me if she told me about a blood test she has gotten done and I said no and then she told me she found out she was pregnant

I didn’t believe her bc she was telling me this all through Snapchat which I had a good feeling she wouldn’t have done if she was actually telling the truth. But she insisted she wasn’t lying and told me she was being serious and being “for real”

I then stopped responding because I was driving and she then messaged me again saying “okay fine I’m kidding hahaha, I just have a vitamin deficiency”

So I was extremely mad because two days prior I was venting to her that I’m having fertility issues and that my ovaries hurt etc.

And she sees absolutely nothing wrong with what she did

I personally think she’s needs to be evaluated for schizophrenia and bipolar disorder because some of the things she says are just not normal at all

But when I talk to my parents about it they don’t see anything wrong with what she does and says.... I try to talk to my mom because my twin smokes weed and drinks on the regular and she says she cares but at the same time she also tells me that she has to wait till my dad is in a good mood to tell him about my sister

There was also this one time when my dad threatened to make me move back home because I don’t hangout with my twin and I told him it’s because all she ever does is try to get me to smoke and drink with her and he told me that it’s MY job to fix it because he doesn’t want to ruin the relationship that him and my mom have with my sister

so my mom claims she cares yet still does nothing about it... and I can’t tell my dad directly because as soon as he realizes I’m about to talk about my sister... like I’ll literally be like “so I need to talk to you about sam...” and he cuts me off and tells me he doesn’t want to hear it and that I need to stop fighting with her (I’m not) and that I need to grow the hell up etc.

At this point I feel like it’s best for my mental health to cut all three of them out of my life... but at the same time I don’t know if that’s too excessive and I’m being selfish