Bowser has only one son?

[Gaia]

Not to mention there are still people who believe Mario came from Brooklyn!

Despite those clashing sources, but he also has italian heritage. Which makes him an american-mushroom kingdom-italian citizen. It's really weird.

this is about as relevant as trying to figure out why Donald has three nephews if his brother/sister doesn't even exist

it's just a way of adding characters that are related to the base character without having to compromise him/her with a wife/husband. Nothing else to discuss here.

And where does Daisy, Launchpad, and Ludwig fit in? They all have close ties, and are considered family friends (along with Gyro and Ludwig von Drake)!

The way I think is that Bowser just took the koopalings under his wing. I see them as apprentices to the Koopa King rather than actual children. Though perhaps Bowser might consider them "children" depending on how close they are.

There's also the "Which came first, chicken or egg?" debates that are going on. Interesting stuff too.