Expect multiple marquee brands from the VW group to feature in F1. Long term rumours of VW and RBR engine tie up, Audi having recent engagement with McLaren, and Porsche looking at a complete entrant as a team (most likely an acquisition). The key thing to understand is on a motorsport level, they all work very independently and having separate teams. So it's likely we'll see multiple brands from the same group.
It'll never happen. Success in F1 will only come with exclusivity on power units and any purchases will come with that clause in there. F1 needs more engine manufacturers if I'm honest, as it helps create the competition.
They will get the same spec engine as that's permitted in the rules, but certainly they're limited by the maps that are provided. Good example of this
is insight from Matthew Carter, former CEO of Lotus Renault.