Who has standing to challenge it? Keeping in mind the courts ruled repeatedly American voters had no standing to challenge the constitutional eligibility of a candidate in the courts.
Nothing prohibiting them from being from the same state. Just a punishment from the electoral college in that electors can’t vote for someone from their own state. And of course they can simply have one of them register to vote in another state to correct that deficit, not like they can’t afford to move. As Bush Cheney did, they were both from Texas in the run up, Cheney registered to vote in Wyoming, problem solved.