I plan to block my whole family on social media.
Why are you going to block them? What will that accomplish?
If I block them, I think it's going to improve my social life.
It's acceptable for them to want to know what is going on in your life. Making your social media account private will only probably make them want to be more invasive.
My life is none of their business.
Blocking your family is a pretty drastic step, as it's likely to have consequences outside of social media. Instead of blocking them, have you thought about discussing boundaries with them? Maybe they're not trying to be invasive, they just don't know what you feel is appropriate.