I disagree that 'brethren' in (Matt. 25:40) are Christians. I believe they are Jews. But, that is no matter.
Whether you believe they are Christian or Jews, they are not immigrants. Which means your attempt to use (Matt. 25) as some rule for a nations immigration policy, doesn't work.
Lees
They do sound like the least of His brothers and they're hungry and thirsty and the O.T. says you have to treat the stranger like your own people and be hospitable.
You shall also love the stranger, for you were strangers in the land of Egypt.
Deuteronomy 10:19
The alien who resides with you shall be to you as the citizen among you; you shall love the alien as yourself, for you were aliens in the land of Egypt: I am the Lord your God.
Leviticus 19:34
‘Cursed is anyone who withholds justice from the foreigner, the fatherless or the widow.’ Then all the people shall say, ‘Amen!’
Deuteronomy 27:19
For if you truly amend your ways and your doings, if you truly act justly one with another, if you do not oppress the alien, the orphan, and the widow, or shed innocent blood in this place, and if you do not go after other gods to your own hurt, then I will dwell with you in this place, in the land that I gave of old to your ancestors forever and ever.
Jeremiah 7:5-7
You shall allot it as an inheritance for yourselves and for the aliens who reside among you and have begotten children among you. They shall be to you as citizens of Israel; with you they shall be allotted an inheritance among the tribes of Israel.
Ezekiel 47:22
Thus says the Lord of hosts: Render true judgments, show kindness and mercy to one another; do not oppress the widow, the orphan, the alien, or the poor; and do not devise evil in your hearts against one another.
Zechariah 7:9-10
You have heard that it was said, ‘you shall love your neighbor and hate your enemy’. But I say to you, love your enemy and pray for those who persecute you.
Matthew 5:43-44
I was hungry and you gave me food, I was thirsty and you gave me drink, I was a stranger and you welcomed me.
Matthew 25:35
Truly I say to you, as you did it to one of the least of my brethren you did it to me.
Matthew 25:40
You shall love the Lord your God with all your heart, and all your soul, and with all your strength, and with all your mind; and your neighbor as yourself.
Luke 10:27