In the event of an unconstitutional order, you are to stand down. In the event of an order which goes against conscience, you are to refuse. If there is an interruption in the chain of command you are to know how you report ultimately to civilian leadership and to which elected official in full capacity. This is all standard material you should be aware of already.
The president is forcing a constitutional confrontation, and these are never times of certainty in how they evolve, but the outcome of such a showdown is certain. The president will be impeached for contempt of congress. If the vice-president remains in defiance, he will be impeached for contempt of congress. This is not the best way, but it is necessary to prevent the emergency from evolving to a permanent tyranny.
You have your orders.