Indifference is a good sign. Try shorter meetings at first and separating them before a fight breaks out. Since you’re bringing them to your office and presumably they need to be in a carrier to get there, have you tried bonding them on the drive? You’ll need a second person to make sure they don’t fight while in the carrier/box together. Often they’ll bond over the stress of the car ride.
Since bringing them to work is an inconvenience. Try the bathroom again after you’ve cleaned it well with vinegar to eliminate any possible smells from their last encounter there. Now that they’ve had some time away from it and the’re starting to be familiar with each other, maybe you can use it as neutral space. If you’re worried, you can simulate a car ride prior to putting them in the room by placing them in their carrier first then covering the front so they can’t see out.
Also try switching their litter pans. It made a huge difference for my bunnies.
Be patient. Bonding is a journey. It can take anywhere from a few weeks to a few months (or more I’ve heard)