No, and no.
BMW have decided that they don’t want to take part in Formula 1 anymore. They’re building cars for the DTM instead, which they feel is more road-relevant to them.
As for Porsche, they’re not entering Formula 1 in 2013. They’re going to Le Mans. Audi will stop racing there because VAG have a policy of not letting their marques compete with one another. Volkswagen have talked about entering Formula 1, but not until 2018.
Neither manufacturer is entering. I don’t know where you’re getting your information from, but I’d stop getting it from there.