Even if the story structure is weak, your design of the characters and their dynamics are really well made. You really did well with the theme of space/ alien school that made me think back on Galaxy High, a cartoon about two human teens transfered to an alien school that sadly only had one season.
I also wanted to ask about Alkaline's past, like childhood, how he enrolled at space school, and what kind of people are his parents, and can you describe the cult they are part of and why they wanted Alkaline on their side?
Also, your story made me want to make an alien story as well, only that being focused on an alien school i'm more into into a found family of a boy being adopted by an alien family and looked for a planet to call home, they left their planet after it being destroyed and the kid was abducted by their ship when taking specimens to study and they decide to adopt him rather than dissect him. He also gets adopted siblings and pets from different planets, they either go to human school or to an alien school ( I think of a mix of UA high school with NASA Space station).
In regards to Alkaline, his childhood was complicated. His Father leaving was tough on him and he had to grow up fast.
It's only his Dad who was a part of the cult, his Mom is at home on Earth with his sister, Joy and is a really fantastic person. How he enrolled in Space School was simply by being a good student and being great at shooting-- that's usually all it takes to be a representative of your planet at the school.
His Dad wanted him back because he was a possessive parent and was convinced his son was part of some prophecy: or at least that's how I wrote it. Truthfully, I think just having a parent who sucks who is trying to get you is compelling enough for a teen to be scared of them.
Anyways, hope that helps flesh it out a bit for you. Thanks for reading!