why do concrete pools develop scaling?

I am sure that you would be able to make it smaller, by pouring more concrete into it, and creating steps.

You can google this information.

I wouldn't recommend it. The above is a good start but isn't complete. Pools have stress working evenly in-to-out all the way around, with most of the weight at the bottom, and basements have stress working down from the edge where it was designed to carry walls. Pools have completely different ...

You'd seriously have to ask an expert that. Like, whoever might put the cover in. It may be possible to build a custom cover, but only the people that make and install them could really tell you after looking at your pool.

An indoor pool is going to be much more expensive to install and maintain. That is why you don't often see them at private homes. A much cheaper option would be to install a pool heater at your outdoor pool so that the water is heated year round.

Show the work your company has done, particularly on steep grades, basements, stairs, and foundations. Anyone can do level flatwork. It takes professionals to do the unusual.