I totally understand your concerns about the loner comment, but the show *has* delivered eight seasons with only two main characters, and a handful of supporting/recurring, and everyone seems to agree it works. Bob wasn't saying there will be no other people in Sam and Dean's life; in fact, by confirming the return of Charlie and Benny, he was saying the opposite. The show is just centered on Sam and Dean, always has been, always will be, and the others come and go. I agree that Bobby, Ellen, and Jo were all absolutely family to the boys, but even they weren't sacred enough not to be killed off. It sounds harsh, absolutely, but that's always been what's so unique about the Winchesters: they lose a lot of loved ones along the way but still go on fighting together. It's not about pushing people away; it's just the nature of their lifestyle.
I'm not trying to imply Benny or Charlie or anyone else currently in their lives (Cas, Garth, etc) won't survive the season, though. Sometimes "coming and going" just means a person is in the Winchesters' lives but not physically present on their case of the week or in most of the episodes. These boys have ties to other people; they're just not around all the time. We've seen them call Garth for help (in the past, we saw them call Bobby), so even if they're not in episodes, they're still a part of their lives. This post was to confirm who would be returning in actual episodes, though.