Spouses can’t share bnet accounts. No adults are allowed to share them regardless of relationship. The only people that can share a bnet account are a parent or guardian with a minor.
Sharing with one minor per account is how it’s been interpreted in customer support for as long as I can remember. I guess don’t know if that would be considered a hard rule or maybe just a guideline, nor that this is something that they would ever take issue with in practice, but for a lot of reasons having each individual have their own bnet account is a good idea.
The only blue I could find is here, though it is not specific about whether this means one minor per warcraft account or one minor per bnet. But as I mentioned, this has always been interpreted to be one per bnet account anytime I’ve seen it answered, and everyone on the same bnet tends to cause issues at one point or another anyway.