What are they? St. Paul?
Twin Cities
There are other twin cities as well such as Sacramento, CA and West Sacramento, CA; or Portland, OR and Vancouver, WA.
"twin cities" btw are two urban areas situated in close proximity to each other that have grown into each other over time. Besides Minneapolis-St. Paul, two other famous pairs of NA twin cities is Dallas-Ft. Worth and Seattle-Tacoma.
However, though, in at least the US, when the "Twin Cities", particularly if capitalized, are referred to and there is no specific context that would indicate otherwise, such practically always refers to Minneapolis and St. Paul.