Hello, this is Dr. Bruce and I would like to help you with your kittens.
Good for you that you want to mentally stimulate them. That is a very important part of their well being.
However, it is not unreasonable to be able to keep them happy even if they never leave the apartment. Depending on their wants, you can provide a very stimulating environment for them even in the confines of your apartment.
Playing with them regularly is very important. Using a laser pointer to encourage them to chase and pursue. Or you can use a fishing pole style toy with a feather or mouse on the end to get them to pounce and chase the toy.
There are also toys that require them to work at getting a treat out of the toy. I also like toys that have catnip in them.
Some cats enjoy the circular plastic toys that have a ball that can't be removed but allow the cat to bat at it to make it go around the track.
It is also important to provide climbing and resting spots at various heights. Window boxes that allow the cats to look out the window are very stimulating especially for cats that like to climb (not all cats do, however).
Making sure to have different types of scratching posts to allow the cats to sharpen their claws regularly also ensure that they engage in natural behavior.
And don't worry about the sleeping. It is normal. Cats will typically sleep 20-22 hours per day even in the wild. It's a good life!
Thanks for these suggestions. We have most of these toys and they particularly like the pole with feather and this gives them a good amount of exercise. They also have a cat tree at the window overlooking a school playground.
There are a zillion different toys that you can get for cats. It is well worth trying different ones because you never know which ones they will like. It sounds like you have a good handle on providing them with plenty of mental stimulation. And they have each other as well. That helps.
My opinion is that it is not necessary to take them to other places to visit with other cats or to go outside. It sounds like you are providing more than enough to keep them happy. Also, if you take them out, then you have to worry about other issues such as fleas, parasites, infection, etc.
Thank you. Your last paragraph has answered my problem which was becoming a real issue for me. If you really do believe there's enough indoor space and they're happy being kept in then I'm happy with that.
I have seen many cats living in smaller apartments than yours that are very content and happy. You are doing an excellent job stimulating them. I don't think you need to worry at all.
Thank you. That's put my mind at ease.
You're very welcome!