*** SPOILERS ****
Read this one and liked. I loved the STEPHANIE's character, how you wrote it.
IMO, you can use MIGUEL's character for more conflicts and thrill. Like he calls the cops or his mom or dad whatever after getting humiliated. This will create more urgency and ticking clock effect.
LUIS is also little under developed. It has great potential. You can build it up that way like it is a major threat than cops in the climax before they see Aliens. And when he is completely changed, it will be good to see the transformation.
FER doesn't add up that much in the story. I mean if he wasn't there, it won't make any difference.
Try to create more tension. Like is STEPHANIE just mentally unstable or really she saw aliens?
And the last thing. Who was DAVID? Just another witness of different incident being interviewed? I think it is confusing to the audience.
These are my personal opinions on what I thought. Hope that helps.