it says to love our brother. who is our brother?
does this mean those in Christ, or all people?

Those in Christ.

I thought that, then was not sure...

But 'love your neighbor' is also written and Jesus answers that all people are our neighbor when asked. (The good samaritin)

Also: 'If you love only those who love you, what reward will you get? Even the pagans are doing that.'

And what is love? 'Love is patient, love is kind. It does not envy, it does not boast, it is not proud. It is not rude, it is not self-seeking, it is not easily angered, it keeps no record of wrongs. Love does not delight in evil but rejoices with the truth.It always protects, always trusts, always hopes, always perseveres. (1 Cor 13)'

The same chapter that says love is greater than faith.