Look.... I don't think there's a nice way to say this, but we're
getting tired of you and your stupid, imbecilic questions. A normal
person could figure these kinds of things out on their own. You must be
a couple of shovels shy of a full load or something. Go away. You are
no longer welcome here.
'Making a cat's life better'.... Oh, brother... Moronic, imbecilic and
idiotic. In your case, all of the above.

                                              IBen

At least they get along together.

Exercise and stimulation.

Carpet covered 2x4s make good exercise equipment. Some people object
to using staples but it makes for very quick and easy carpet
wrapping of 2x4s using an electric staple gun. If necessary, you can
cover the staples with glue or something. Shelf brackets can be used
to mount your 2x4s along a wall, preferably next to some windows.
Instead of screwing into the 2x4s, you can use some thin rope to
secure the 2x4s to the shelf brackets. My cats very much enjoy
climbing around on carpeted 2x4s. All you need is some 2x4s, some
inexpensive carpet, and an electric staple gun (about $30 USD). It's
quick, easy, and flexible. Don't worry about precisely how you're
going to use the carpeted 2x4s, just do it. Cat food works great for
encouraging them to climb. Climbing for food can help keep your cats
healthy too.

I would emphasize that one.

For stimulation, keep a window open without letting the cats outside
(of course). Give them a comfortable sleeping place next to the
window. Let them use their senses of smell and sight.

If the room has no windows, maybe use an infant room monitor, with
the transmitter placed outside, and with the receiver connected to
decent computer speakers. But keep the volume down at first and look
for signs of too much stimulation later. It's exciting and probably
not good for a cat suffering from anxiety. How exciting probably
depends on what sort of sounds there are in the neighborhood, like
occasional people sounds versus lots of dogs barking.

Good luck.

In case you didn't already know. Keep in mind that in the animal
world, things happen very quickly. A dog can kill your cat before
you have time to do anything about it. If something goes wrong with
the introduction, if you are lucky you will have time to exert great
physical effort to remove the cat from your dog's mouth before it
dies.