Its best to start with a smaller room or section of a room that you can bunny proof thoroughly. Electric cords should have cable covers. House plants should be placed out of reach. If the floors are slippery, they should have rugs or similar that provide traction. Place their litterbox where you think theyll want it but be prepared to move it if they decided on another spot to go potty in. For a larger area, provide additional litterboxes to prevent accidents.
Supervise at first. Rabbits are a lot more agile than they might seem 🤣 They can climb up on the backs of chairs and sofas to reach window sills, jump up on tables, chew baseboards and wallpaper and carpet, squeeze into narrow spaces. Its difficult to perfectly bun proof an area until you see the buns in action in it. Be prepared for extra marking poops outside of the litterbox. Cover sofas and other soft furniture (bed, armchairs) with easy-to-wash blankets in case of accidents. Many rabbits like peeing on sofas and beds.
Obviously provide hay, water and a hidey-place, f ex a cardboard box or just a foot stool or low bench that the rabbits can use as a “safe” lounging spot.
My buns have all been not neutered at first when I started to free-roam them.