The B path is just Sho never visiting his mom. Whatever you choose as Saya's advice Is something else, not another route of it's own. I get that Yuu said he felt uncomfortable in the C route without the need of Saya's advice, but in the A and B paths, just ask Saya for relationship advice, simple as that.
The routes are good, neutral, and bad for a reason.
Good: Sho visits his mom. This is A. Neutral: nothing happens. This is B. Bad: Sho quarrels with Yuu. This is C.
The developer said the "Saya's advice" desicion will most likely only affect the route until nearly the end of the game (whenever that will be), which means there may be A 1 and 2, and B 1 and 2. As stated before, Saya's advice is it's own thing separate from the 3 important choices in Sho's route. I really hope its stays as A 1 and 2 and B 1 and 2, because having endings A - E may be a bit overwhelming (not just on the players, but on the developer themselves as well).