I would say that you are barely an adult and you haven't experienced everything life has to offer before kids. Being siblings with many kids isn't the same as being their parents. Though I'm sure you know that. You working a part time job and him working a full time one isn't a great financial situation as you both are young with little to no work experience so I don't assume your pays are good enough to support a child along with you two. You two should enjoy life a bit more before having kids, I think.
There's so much personal growth you both need to do to be able to provide your child(ren) with a good upbringing. My mum had me and my brother when she was 18. Sure she and my dad had jobs, barely enough money to get us by though, and they spent most of their lives at work trying to support us. We barely saw them at home. Not to mention the emotional immaturity both of them had. I'm not saying they weren't maternal and paternal, that they didn't have good parenting instincts. Not at all. I'm saying they had no time to work on themselves and get over their own childhood traumas before having us, they had no time to research how to bring up children in a healthy way, they had no idea what it was like to be just with themselves.
The end result? They passed their own childhood traumas onto us, me and my brother had awful communication skills and problems with our own relationships later on that stemmed from our childhood. We still do. I am angry with my parents for it. My father was the worst, I barely talk to him because I can't stand how much he messed us up. I didn't have to go through all this just so they can have kids, that's very selfish. If only they had us a few years later they would've known better, about themselves and how to bring up kids. And both of my parents were from massive families. I have countless cousins.
You can really ruin your children's entire lives by not being emotionally and mentally ready for children. And at 18 you're definitely not ready, mentally. You need to figure out who you are first, you need to find your faults, you need to find those parts of yourself that could be harmful for your children and actively work on them. Take classes, learn about the psychology of child development.
I know you want kids, and I understand. But there's no need to rush. There's so much to life other than kids, and after having kids you're very limited on what you can actually do. Please take some years to work on yourselves, to improve who you are and get over those traumas. Your children will thank you for it.