The non-pregnant bunny is probably experiencing a false pregnancy. That can happen when a girl bun interacts with a male bun even if they don’t have direct contact. The pregnancy-hormones from the pregnant bun can also set off a false pregnancy in another bun. This is not uncommon. The falsely pregnant one also has a surge of hormones that makes the fur on her chest loosen so it’s easily pulled off. You can give her a nest box as well as the actually pregnant bun. The pseudo-pregnant one won’t of course have any babies, but letting her build a nest can relieve her of some stress, her body is convinced she has babies on the way. Pseudo pregnancies resolve on their own.
The pregnant bun will give birth very soon, probably by tomorrow, gestation is 31 days in buns.
Don’t throw out the pseudo-pregnant bun’s pulled-out fur in case the other bun will Ned it as bedding for her kits when they come.

This is an odd coincidence! My feral foster bunny kindled a few days ago! I though she had tumors when I felt her stomach, turns out she was pregnant! Good job properly diagnosing your bunny, with a case of kits!? As Bam stated, provide both bunnys with nest boxes, and lots of food for the actually pregnant one.