You have begun the journey of becoming a true slave to rabbits. It always is the human that has to make the changes instead of rabbits changing their behavior. (as rabbits are just rabbity like that, and they aren’t going to change in some ways)
Just know that until they get to know the surroundings, it is part of their instincts to get into every nook and cranny of your place. It’s just the nature of being a prey animal. They map out the place, and once they know it, they will notice anything new. It’s curiosity and survival instincts combined. So once they’ve gotten the comfortable with the lay of the land they may settle down a bit.
I think that it will also be important to supply something to catch their interest and distract them — things to chew on, toys etc. Boxes and tunnels they can go into are a big favorite. Also check out the homemade toy section https://binkybunny.com/BUNNYINFO…fault.aspx for ideas too. If they are playing with those things, they are spending less time getting into to trouble.
Now onto the specifics you’ve noticed:
1. Bunny on the nightstand–That one just sounds funny. Sorry. I would have loved to have seen that. Are there things on your nightstand that he could chew? Is it high and slippery, unstable? While your bunnies are playing put something on your night stand that would block their access. In time, they may get used to not being able to go on there that they would eventually not even try. That is more along the lines of how my bunnies learned. (Also, age mellows bunnies too)
2. Cardboard anywhere is fair game. — If you are unable to store them out of the way, you can use NIC cubes/Organize wire cubes, connect them together to cover the first foot.
3. Flower and plants that are toxic should be out of the a bunny’s way. So during your rabbits playtime out, move the flowers to a safer place. Even if the plant was non-toxic, no one wants a chewed up plant. I use hanging plants and plant stands. I do not have any plants where my bunnies can get to them.
4. Unless your bunny is causing damage to the chair, and is just sitting there, I don’t see any problem with it. If you are able push the chairs into dining table itself then would that prevent them from accessing the top of the dining table?
5. I am not sure I understand the problem of jumping through the piano legs? They are not putting his feet on them as they pass by right? Just fur would brush by. I may not be picturing this correctly. If you find them wanting to chew on the furniture legs, then that is another story and there are tricks to help avoid that. Some people have had success with rubbing soap on, there is also some apple bitter chew deterrant you can put on areas you do not want them to chew. However some rabbits really like the bitter taste. There used to be an apple bitter cream that
One thing you will have to watch closely for is if they pee on your couch and chair as that is not uncommon for some bunnies. If they get up on the couch and you see one begin to stand still and then lift its tail, say No and shoo them off immediately before they have time to follow through. I was able to train Jack not to get up on the couch at all by watching him closely and the moment he looked like he wanted to jump on the couch, I’d say no. (He understand No). With persistance, it worked. If he was a bunny that I could trust on the couch, I’d let him up, but I never could. He would pee or chew on the couch.