I have only told 2 family members, my mom and my aunt, my dad doesn't even know. I find it easier to tell strangers than it is to tell my own family.
They shouldn't judge you or be against you taking care of your health.
Wait until you have a date, until you start liquid diet, which I assume you have to be on, I didn't, but in the US, everyone does. It will give you more time, but also more information from your doctors etc. to inform them why this is something you want to do.
Good luck, best decission I ever made.