Can I adopt a u.s citizen and become legal in the US?
No, adopting a child is unrelated to citizenship.
No. Adoption doesn't have anything to do with becoming a citizen for the adoptive parent. In fact, to adopt you have to have US citizenship already or be a legal permanent resident. You have to follow the same immigration process everyone else does to become a legal resident or naturalized citizen.
No, it doesn't work that way.
You can't even adopt if you're not a us citizen
Heard of DACA? Look it up. Same issue.
No. However, there are lawyers who might actually try.