No, VW owns all the other brands plus Rolls Royce, Lamborghini, Bugatti and a couple more.
Porsche is still a bit more independent, although VW swallowed them up after Porsche's takeover of VW failed for political reasons. Porsche gambled on the EU shooting down the 20% blockade minority the state of Lower Saxony holds at VW. They lost.
On a sidenote, the biggest shareholder of VW is still the Porsche family. Mr Piech (VW) and Mr F. Porsche (Porsche) are cousins. Both are grandsons or so of Ferdinand Porsche, the company founder who developed the VW Beatle. So it was a bit like Dallas, but with cars. ;)
The story behind the firings is actually quite simply:
1) CEO has to go. Of course.
2) CEO of VW USA has to go too, of course.
3) The Porsche head of R&D and
4) the Audi head of R&D were the heads of VW R&D during the relevant time period. So both were fired because they were either responsible or should have prevented it.
5) VW, Audi, Seat and Skoda all use this TurboDiesel engine for a gazillion models. Platform technology FTW! Porsche usually develops their own engines, apart from a few cooperation for their non-standard cars. So if they wanted an in-house solution, only the Porsche CEO could move to VW, because he is with high probability not involved in this clusterfuck.