They will need more than just a little bit of fur to keep warm. You can add things like teased cotton balls, dryer lint, feathers, or even fur from other rabbits.
If the doe does not mind being handled, you can pull fur from her belly, rump, and sides. It should come out fairly easily, just pinch a bit between your thumb and forefinger. Pulling fur will also help her milk to come in and generally jump start her maternal instincts.