זה חריף בשבילנו should be accepted, reported.
Translation in english should say "this is spicy for us!"
Yeah it's awkward the way it was presented
I think it can be correct to say "for us" at the beginning of the sentence, depending on the context. "You may call this mild, because you are used to it. _For us_this is spicy. "
בשבילנו זה פיקנתי I think 'picante' is used more often in colloquial Hebrew
It's used to mean "spicy-ish", a bit tuned down. פיקנטי.
Is זה חריף לנו completely wrong?
No, there is an implicit emphasis when changing the word order,but should be considered correct.
Why את זה incorrect in this sentence?
Because את is used only before a direct object. Here, the "this" is not the object, but the subject of the sentence.
For our sake this is spicy.