You are right: they are our fellow humans.
But there is a distinction between a citizen, a non-citizen who is legally there, and a non-citizen who is illegally there.
What do you prefer to call a non-citizen who is illegally there in this context?
"Alien" has been the go to word in Englishf or a long time.
You know what every ...[text shortened]...
In English, it is called an "Alien Registration Card."
This is not abnormal language at all.
A few years back, here in London, we had several days of riots (fuelled and organized via social media). Quite a scary time with buildings being set on fire and shops looted etc. On one day in particular, the area where I live was targeted and the streets were full of police and determined looters.
Anyway, we heard a commotion in our back garden and discovered a young chap had jumped over our wall and taken a bad fall. (Probably trying to flee from the police). I guess I could have viewed him as an invader or an unwelcome alien who was there in my garden illegally. I could have declined to offer him medical help and immediately reported him to the authorities to have him removed.
I didn't of course. While I helped him attend to his wound (a nasty gash on his leg) my wife made him a cup of tea. - You may disagree (which would be odd seeing as I am the atheist and you the theist), but as a 'fellow human being' I felt obligated to help him, even though he wasn't meant to be there. I'd even go as far as to say that he had the 'right' to receive my help, purely on the grounds of being a 'fellow human being.'