YES.
No, you can't use ps2 controllers to play ps3.
About 8 controllers
no
No the PS2 controller does not work on the PS3 you need an adapter which is like $15
2 controllers can fit in the playstation2
The PS2 game will probably work, but the controllers/peripherals probably won't.
No. The PlayStation 3 doesn't have the PlayStation 2's input sockets for the controllers. However, Sony were planning to release a USB adaptor for the PS3 so that you could use your old controllers. It was never released, and is never being released in the UK, but I'm not sure about other territories such as the US or Japan.
You can connect up to 7 controllers. And if people want to use the PlayStation Move while playing, (using 2 controllers) you can have 3 people using it, and have 1 person using the original controller, or 2 people using PlayStation Move and 2 people using original controllers, and etc.
Yes they do. It works the same with PlayStation games on PlayStation 2 consoles.
You can use two wired controllers on a PlayStation 2. Then you will need Multi-Tap and two more controllers (wireless).
Yes they are
It enables up to four controllers to be plugged in to the PlayStation 2 simultaneously.