I feel like people generally know if they have a family history of these things, or maybe that’s just me?

It's certainly not a given that someone would know.

Maybe, maybe not. There can be a lot of surprises in one's family history. And it's all surprises if you're adopted.

Okay, but most people are not adopted.

Schizophrenia is a genetic disorder, so if you parents or grandparents have a history of it, then that would indicate a genetic propensity for it. I am sure there are also relevant SNPs you could look for if you have your genome decoded.