How to hide my true feelings from my family?

Faking being okay only makes it worse I promise you from personal experience. You need a safe space to talk about why you aren't okay, whether it be one person, multiple people, your family or a girlfriend or best friend - someone will listen to you. People who love you don't want to see you drown from your own problems, they will want the opportunity to help you

It is okay to not be okay. And while it may not feel comfortable talking to your family about your struggles, it is important to have a safe space where you can talk about it. One of my safe spaces is seeing my psychotherapist.

Is your family mental health positive? That will affect my advice

I don’t think you should hide your struggles from all of them. Choose someone that you’re closest to and let them know what’s going on. I know how hard trying to hide everything is. It helps to at least have someone to confide in. I hope this helps