Diplomacy - Movement question
If these are all orders from one country, nothing happens.  From the rules:


  A country cannot dislodge or support the dislodgement of one of its own units


If "F StP -> Nwy" is a different country from the other two orders, the unit in StP is dislodged.  From the rules:


  Support is cut if the unit giving support is attacked from any province except the one where support is being given.