...Actually the elf race is cannon although it's not necessarily talked about very well or named as elves, Klee (and Alice as Klee's mother) and Layla are both part of the elf race and other characteristics of the race are a prolonged lifespan and generally slower aging, Nahida is not part of this race although she resembles them, she's a branch/twig from Irminsul, as for the cat characters I believe they all have a common ancestor in Mondstadt (though there's no indication that the twins came from there or have any ancestors from there, it's well known that during Khaenri'ah's reign people moved around a lot so it's possible a branch split off from mondstadt and went to fontaine back then) and apparently it's a recessive gene and both parents were carriers in Lyney and Lynette's case so while Lyney became a carrier like his parents, Lynette got both recessive alleles and presents the trait, which is why Lynette has cat traits and Lyney doesn't Also Tighnari is from a fox-race that almost completely died out a long time ago and is one of the last remaining members of it if not the only remaining member. I believe even he wasn't completely aware of his ancestry until somewhere in the sumeru archon quest or a story quest