[hocus pocus]

This is not your fault at all.

I think you should consider seeing your guidance counselor. I highly doubt your counselor will tell your mom or your grandmother anything, especially because what you say to your counselor is supposed to be confidential. I think seeing your counselor can do you a lot of good; just talking about things sometimes can be really helpful. If you're nervous, maybe you can send your counselor an email or write a note instead. Perhaps you can talk about wanting to switch schools and see if your counselor has any information that can help you.

Your sexuality is yours. It's not your grandmother's, or your mom's; it's yours. If you want to be open about it, then go ahead. You don't have to listen to your mom and grandmother if you don't want to. Do what makes you feel comfortable.