"Where does it say that we should take care of our brethren first"
Galatians 6:10
"Therefore, as we have opportunity, let us do good to all people, especially to those who belong to the family of believers."
I think that this also fits with what Jesus Taught: -
Matthew 22:37-40: - 37 Jesus said to him, "'You shall love the Lord your God with all your heart, with all your soul, and with all your mind.' 38 This is the first and great commandment. 39 And the second is like it: 'You shall love your neighbor as yourself.' 40 On these two commandments hang all the Law and the Prophets."
If you cannot love yourself, then how can you love your neighbour.
The same is also true for doing good to all people, if you cannot do good to those who belong to the family of believers, then how can you do good to all the people?
In other words do not differentiate between the people living around you and the brethren when doing good.
It was my advise to the people in the third world country where the Goats were being given to families. not to differentiate between the "Christians" and the people of the "other faiths" that the Christians were living among.
There is a fine line of responsibility when doing good to all.