If I write:
Only a few of his friends were are at this side
is this correct? Or should 'were' be 'was' as a few is singular?
I must first correct another part of your sentence: you wrote were are at this side – I think you meant either
Only a few of his friends were at his side.
Only a few of his friends are at his side.
In this structure of this sentence, few is an indefinite pronoun referring to friends, and since friends is plural, you use were and not was.