Spanish tutorin

Grew up in home where parents speak Spanish. I understand some but I can't speak it.

If I got a one-on-one teacher to teach me it, how quickly would I learn it considering I grew up in a home where my parents spoke it? I'm an only child so I don't know how anyone would've fared if they lived in the same house as me.

Why don't you know Spanish? How does that happen if your parents just speak Spanish?

My friend said he doesn't really speak it either but understands some of it. But his sister, brother, and parents all speak Spanish at home because they're from South America.

But me and one of my brothers were born in the US and my sis, other bro, and parents are from Mexico. So me and my bro grew up in the US but we know Spanish.

WtF?

Whyyyy????

And you would probably learn it quite quickly if you pay attention and don't just spew out English automatically like my friend does.