Rune Factory/WMG

Neumann is Nicolas' biological father.
Sabrina can try all the handwaves about "We were only married a short time" and "before I had Nicolas" she wants. Ain't buying it. Also not buying Neumann being friendly with Nicolas just because he's Sabrina's son.

You start Chapter 2 with 0 relationship points with your own mother because...
You remind her of the husband who ran out on her without a word seven years earlier. You can win her over, of course, in the usual way (bribery).

Gaius is only laid back because he's missing an eye
Maybe I'm reading into it to deep, but he mentions that you can't be to impatient of hard with stone, and that his eye is proof of that. He used to have a personality more like Zaid's before he got that injury, and took a lesson from it and mellowed out.

The Selfia Kingdom is without a prince/princess because...
The old princess ran away to Trampoli and became a librarian. Other than that she was once a princess, Selphy's backstory is woefully underdeveloped; it's not even expanded upon in the Official Memoirs. Why not mention it there? It's a plot point later on. The women in the royal family, of course, are all named for the kingdom. Or the kingdom is named for the women. Either way works.
 * And since it's been revealed that side-character Roland (whose name was changed to Nolan in the localization) is the king of the Kingdom of Roland, it isn't too farfetched an idea.

The plot will heavily involve Vetuswill, the Dragon God of Wind.
Terrable (earth) was the Big Good of RF1 (with a false Fiersome being a Bait and Switch Boss-type). Fiersome (fire) was the Big Bad of 2. Aquaticus (water) was the Jerkass God of 3. RF4 will obviously feature a quest to find and/or restore the fourth Dragon God.