The Flash vs Terminator Genisys

[floramon]

I understood the 2015 TV series The Flash time travel paradox, and I agreed with Dr Wells, "If you changed the past, you may get same or even worse disaster in the future."

That's why future Barry stopped Barry from saving his own mother.

In Justice League Flashpoint Paradox, Barry saved his mother but caused the world to end.

However, I totally don't understand Terminator Genisys. How the hell could they change and create timeline? And there were no consequences from their actions?

For example, yesterday a car knocked down my cat. I traveled back to yesterday, stopped the accident, tomorrow my cat is still alive, and the world remains the same.

This is totally BS, right? How could you change an incident without changing the world?

In Terminator Genisys, what happened to them? They could not return to their own timeline and world anymore, they were stuck there (just liked Reverse Flash stuck in Barry's timeline).

How many terminators did they send back? Who the hell sent Arnold to save 9-years old Sara? Who the hell killed 9-years old Sara's parents?