The answer to "can I use "who are" in a sentence that is not a question?": YES
I think that the entry in the Cambridge Dictionary is very informative and it got a lot of examples of that particular use
who pronoun (USED TO REFER)
used as the subject or object of a verb to show which person you are
referring to, or to add information about a person just mentioned
I think it was your dad who phoned.
She's one of those people who love
to be the centre of attention.
He called James, who was a good friend
as well as the family doctor.
But you asked particularly about "who are". Some examples that I've found in a quick search
Announce an immediate and unconditional amnesty for all those who are imprisoned for political reasons.
We represent all the citizens of Europe not just those who are organised in NGOs.
I think you should not play with guys who are not kick the ball like you
is not correct. "are not kick" is not a valid construction.
This one is correct
I think you should not play with guys who are bigger than you
Maybe what you were trying to say is
I think you should not play with guys who don't kick the ball like you
do is the auxiliary verb used to negate kick