You can take family law classes when you're out of your 1L year if your school offers them, but you still have to take a huge required curriculum that has nothing to do with family law. You will also have to pass the bar which may have no questions on family law.

My school does "concentrations" where you can pick either criminal law, family law, contract law, etc. It's not a minor like in undergrad, it's just a signal that you took all these specific classes for electives that show you are probably good in this area of law.

Only go to law school if you want to be a lawyer. You'll waste a lot of time and money if you don't. There's a lot of schools that do MLS degrees with a concentration in family law. There are tons of government jobs in family law that if you get an MLS you'll be the top candidate.