Here's what I found, from a cycling club site:

Car Approaching from the Rear:

Two Riders Side-By-Side:
Cyclist on the left accelerates past the cyclist on the right and moves over to the right-hand side of the lane. The cyclist on the right slows slightly to let the fellow cyclists get by.

Multiple Groups of Side-By-Side Cyclist:
Each cyclist on the left accelerates past the cyclist on the right and moves to the right hand side of the lane. The cyclist on the right slows slightly to allow the passing cyclists to get by.

Group of Three Cyclist, two side-by-side with a third cyclist in the center behind the other two cyclists forming a triangle.
Cyclist on the left accelerates past the cyclist on the right and moves over to the right-hand side of the lane. The cyclists on the right slows slightly to let the fellow cyclists get by. The third cyclist in the triangle drops back behind the second cyclist.