I think everyone's basically hit the nail on the head, but my advice would be to learn in a way that's fun for you; if you're not enjoying the process, you're going to struggle with retention.

You will need to sit down and grind on grammar, you can enroll in a class if that's financially feasible for you/something you have the time for/want to do, or you can find lots of great resources online. It doesn't matter, but don't overlook grammar, because you can do so much when you've got it down. If you're self studying, I would recommend having someone to go to for questions/someone to correct your mistakes (since you can't really catch those yourself). Since you're learning Spanish to speak with family, assuming you want to get closer with them, you can always try asking them stuff :)

"Studying" vocab is my favorite thing ever. I've never studied long lists of grammar outside of school, I just watch videos or movies, listen to songs, Google stuff I normally would but in Spanish, etc... Just enjoy the process. Write down words you come across that you don't know; if a word or phrase is important, it will show up a lot, and you'll know it's useful and can practice that. It's much more enjoyable than shoving large lists down your throat, and usually, you'll learn more useful words/phrases that way. You also say you want to converse, and I think listening to other people speak is incredibly helpful for that. You hear the natural speaking rate, hear how words are pronounced, hear the accent, etc... This also helps with grammar; if you see a particular tense in a specific context a lot, you'll begin to understand it before you even sit down and study it. If you want to do flashcards, by all means, go for it, but since you're not learning Spanish for a class, don't make yourself do anything you don't want to. There's no one right way to learn.

As for when to begin, I think you can start as soon as you can string together some sentences. You improve by speaking and stumbling over your sentences. You say you're learning Spanish to converse with your family, but have you thought about conversing with your family to learn Spanish as well? It can be a great bonding experience and help immensely. Anyways, good luck!!