I don't understand the Nintendo Switch. How many do I need for a family of gamers?

They are a personal device like a gameboy.
There is a TV version for party games.
The games may or may not be shareable, even with the physical games.
Assume the ideal usage is during screen time on a weekend.

I have been avoiding buying one as I don't understand them. Thinking of getting them soon.

I assume one OLED for the family and then a portable per person, then one copy of each game per device.

How is this affordable?