Why am I not able to change my password

My annoying siblings have discovered my pin, and obviously, I wanted to change it, but when I go to settings and then the privacy part, it asks for confirmation. So I have to type in my password again, but when I type it in, it says that it is incorrect, even though I literally just entered my device with it. I closed it and turned it on again, I've tried multiple times and yet it still says that my password is incorrect. Please help, I can't deal with my siblings torturing me everyday and going through my personal stuff.