This can happen with teens even when they’re not stressed-out seniors applying to college. I read the best book about it called “Get Out of My Life, but First Can You Drive Me and Cheryl to the Mall?” It’s an older book, revised over the years, and the author has written a newer follow-up. Note-this book and my experience is just about having a mouthy teen who thinks parents are on the stupid train and that teens know it all.
Just had a moment with my own senior. After being mouthy all afternoon, I said, in as calm a way as possible, “I don’t know why you’re acting this way today, but you need to dial it back.” And she did, because she genuinely hadn’t realized how nasty she sounded. With her older sister, that didn’t work, and things got so contentious that we DID end up in counseling. It was very helpful having a neutral 3rd party help us use non-threatening words to hash out differences. It didn’t make things magically perfect, but it helped.
It sounds like you’re not a native to this country, OP. Perhaps some of the hostility you’re experiencing is your son wanting to be more independent than you’re used to and he’s frustrated with the differences between you. That doesn’t excuse rudeness, but it does possibly explain it.
I agree with the above suggestion to have a heart-to-heart, calm talk and explain what you will and won’t pay for regarding college. Remind him that his essays play a part in where he goes, and that he should have SOMEONE look them over. Then drop it. Hand him a list of the in-state public colleges you can afford and that may not even HAVE an essay component (many in my state do not) and tell him that unless he does a good job on the essays, his options may be limited.
I know it sounds counter-intuitive, but when they act like this, you just love them even more. It’s when they need you most. Maybe he’s scared to leave you alone to care for his sibling. Maybe he doesn’t actually want to go far away. Maybe he is being pushed to major in something that he doesn’t want to do, or go someplace he doesn’t want to go. Maybe a bit of all of that. When teens, especially boys, get scared and/frustrated, they lash out at the people closest to them. I don’t think seeing a therapist is a bad idea.
The good news is that they eventually come around and become nice people again. My son was a different person after his time in the military. He grew up so much between 18-25. MY older D was a bear between 16-19 but at 25 she’s a sweetheart and we’re very close again. MY youngest is a different kind of kid, but even SHE has her moments. Be firm with love and respect-it will all work out. Good luck.