Legal is an acceptable term right? No one bats an eye at "Legal Resident". What's the opposite of legal? Illegal. As far as I think, these are just states and do not imply anything about the person in question. They are terms I assume used pretty ubiquitously in most places of the world with a government in different forms.

Again, as far as I think, being somewhere illegally doesn't make you any lesser of a human than I am. But they are still here illegally. I could call them undocumented too, but they're still here illegally.