I wonder if anyone's ever tried to give the fanmade surnames, but actual surnames that sound like they could be surnames, and not just whatever their species is. A good idea would be to take a leaf out of Final Fantasy's usual book, and try to make them sound like surnames, but also have them be something relevant.

I mean, I don't know if they all are, but Final Fantasy tends to give its characters names that relate to that character, but still take a bit of thought to understand, like it relates to their storyline or their character, be it a word that means what they're referencing or something else, like... a name shared with someone who was a similar character to them or something. So basically find a word or something that fits with that character or something (Guados and Ronsos can be included), and turn that into a surname - you can change it up, or keep it as it is, as long as the meaning doesn't jump out too much, unless you are overly familiar with the meaning.

Again: I have no idea where the idea of Seymour Solus comes from (maybe that was fanmade all along?), but according to The Final Fantasy Compendium, "solus" means "alone and ignored", which they liken to his backstory.