Hypothesis: Alice Moonlight entered the UAA within the three years between NMH and NMH2 alongside her sister Margaret (so the ranking screen in the NA version listed her original registered name). She then met Mr. Twilight and married him, which changed her surname from Moonlight to Twilight.
A different interpretation is that she already had a relationship with Mr. Twilight before entering the UAA and only married him after the initial registration.
The child is a separate hypothesis: he could have been from Mr. Twilight's relationship with a previous woman, OR adopted by him before he met Alice, OR was adopted by them after they married, OR even their biological son out of wedlock years before her UAA entry. Someone should ask Suda51 about Mr. Twilight and Alice.