I think there aren’t rules for this because no one anticipated that the Dems would try to collapse the government if their candidate lost.
The joint session is controlled by the two chamber leaders, therefore it’s on Paul Ryan and Mitch McConnell to prevent idiocy from occuring.
Each person’s ID should be checked at the door, and looked up in a databsae. If it is not obvious that they are a citizen they should be detained until this can be verified. Anyone found not to be a citizen should be handed over to ICE and deported.
We’ve already had Latino terrorists attack the US Congress once, let’s not let it happen again.