So even though everyone fits in the existing modules there is no spare if they let these two go home.
Boeing has stranded these astronauts on the ISS because it has no (acceptable) means of bringing them down, and the astronauts themselves have no personal means for doing so. If they want to become un-stranded then somebody will need to arrange the means for them to come down.
That doesn't mean that it's impossible for somebody else to provide those means, or that the means simply don't exist in any capacity. But they meet both the dictionary and common colloquial definition of stranded.
That's like saying that after 9/11 when all flights were grounded and you, as a New Yorker, weren't "stranded" in London because, hey, you could always row a boat back. It's such a weird and meaningless semantic defense.
Why are you defending Boeing here?
The answer is here: https://news.ycombinator.com/item?id=41470523