Take the water and rocks from your tank and put them in the other tank with a heater.
In the meantime, remove the rest of the rocks and put them in a container with more of the tank water. Try to save as much tank water as you can.
Remove all of the crushed coral substrate and toss it. Put all of the rocks back in the tank laid out like you want it. Then put in the new sand. Don't buy live sand, just get dead, small particle sand. Sugar size aragonite is nice.
Once all of the rock and sand is in start to fill it back up with the tank water you saved, Have some newly mixed, same salinity, same Ph, same temp water on hand to top off the tank with.
Once the display is set back up with the new sand, old rocks, and as much old water as you can, let it run a couple of hours to stabilize a little.
IMO you will then be safe to re-acclimate your fish back into the newly setup tank.
Good luck with this and keep us posted with pics if you can.