Questions from Babbel.com

[Jacob6503]

Hello,
I have a few questions that have come up while studying on Babbel.

Por qué v.s. por qué aquí
I understand the second may mean "why here" but is there another meaning to it due to the aquí?

I am learning frequency of time, for example "dos veces por semana" or "una vez al año". Is there a difference between por and al here?

Lastly, the sentence was "¿Os estaís ocupando de todo?". What significance does the "Os" have here? Isn't "Os" reflexive?

Thanks for any help you can offer,

Jacob