Responses

I don't get what's so confusing Σ(  ̄□ ̄||) In Japan, mothers call their child by their first name. Nanasuki is his last name, while Ryousuke is his first. So that's why the mom calls the MC him that, while others tend to default to Nanasaki to be polite... And his husband and him just so happen to have the same first name too. So essentially, the couple's name are Ryousuke and Ryousuke, with their kanjis just being different.
this is so cute but wtf is his name then the mom called his ryouske and he's called nanatsuki but the husband was called ryousuke ... anyways still a very cute and interesting story