Rainier anytime is a hardcore mountain.
Their route of choice is one of the least technical, that makes me wonder if their choice indicates a lack of technical climbing experience since they picked the "easy way". Many more experienced climbers may have considered Disappointment Clever to be a little bland even in winter.
Winter on Rainier can be sick. Its proximity to the ocean gives it huge storm and snowfall potential.
Sorry to hear they are in trouble I hope the rescuers all get off safe either way.