Dude, there should have been reinforcements sent the moment the prince was found poisoned, no need to inform the troops of the poisoning, just send back up to the twins. Soldiers follow orders. They waited until not only the prince was treated, but let the other prince send a message and causally stroll down to check what was happening, and instead of keeping the King informed, just try to handle it on their own. Maybe the people conspiring are counting on that lack of communication and exploiting it. Then I remembered that all these royal princes had some weird magic growth spurts and are actually still very young children. This is just a bunch of little kids acting like adults.