I must have missed this response when you first posted it.
Sell them out of the same showrooms? Porsche is just a VAG brand now, no reason to not have them share space with Audi.
When Porsche was an independent company, it made sense to broaden the base. They don't need to do it now. The Panamera, Cayenne and Macan space can easily be filled by the A8, Q7 and Q5. The latter two are platform mates with the two Porches as it is as it is.
Porsche sales are also down because of the continual move upmarket.
There's a reason that the automakers have moved away from sharing showroom space with other brands. It compromises their branding, marketing, messaging, etc.
Even as a subsidiary of a larger group, a brand still needs to pull its own weight. Generally speaking, there's little point in subsidizing other product lines.
There are also significant differences between the Porsches and Audis you mention, and the Porsches are without exception significantly more expensive than their Audi brethren.
I'm sure the move upmarket has affected sales but there's no question that the sports car market has been suffering for a while, and will continue to do so.
