What type of orchid,s are they? hardy or tender?

If they're Moth Orchids, (Phalaenopsis), then cut the dead stems back to just above the bottom node (the little 'flap' you'll see). You should get a new stem of flowers either from there, or from between the leaves. Be patient, but if they're a bit slow, put the plants into a slightly cooler room for three weeks, then bring them back. That usually does the trick.