So my parents do not understand why I want to come out to the rest of my family and they think that coming out is stupid and pointless. How do I explain it to them in a way they will understand?

You can tell them that it's a big part of who you are and it's ok if they don't feel familiar with the idea of coming out, because they never saw people assume they are something they're not, so it's ok if they don't understand what it's like. That's why they should trust you on this. After all, it's just like when there's something big going on in their life and they feel the need to share it with the people that are important to them: the same goes for you. And even if they don't see the point, coming out is not gonna harm anyone but it's gonna make you feel better, so there's no reason why they should oppose it. You can try to tell them all of this, and of course, encourage them to share their thoughts and tell you why they think so. If they see you so open to reasoning with them, maybe they'll be more open too.