Great to know that!
Yes it's definitely possible. Try doing a LinkedIn search for people who worked at FB first then at Instagram
Absolutely for SWE. One data point, a friend of mine made the switch, then switched back to Facebook a year later.
Why did he switched back?
Cited a lot of NIH, cluster fuck of tech, dissatisfaction in code quality and leadership.
Depends on the role, but it's possible and I've seen a bunch of people do it.