As others have said, yes, all the same resort complex with shared pool, restaurants, movies on the beach, shops, etc.
We've stayed at both - BC many times over the past 21 years and YC just once last year. We prefer BC because we like the theme and decor at BC and the proximity to BC Marketplace (which offers a nice selection of CS food, groceries, merchandise and a self-serve refill mug station.) BC is only a tad closer to Epcot, but that helps too. We did see quite a few convention attendees at YC, so it has a slightly less "vacation" feel for me. But I still think YC is entirely child-friendly. For us, the most significant benefit of YC is the guaranteed full balcony. But we've requested and received a full balcony at BC for every stay (and there have been many!)
In the end, I love both and would not hesitate to stay at YC again if BC was not available!