why do leo and tusk have animal names but not sera and amu
Actually, they do. Sela (yes, that’s the correct spelling) comes from selachii, the branch name for sharks. Amu comes from Amur tiger, more commonly known as the Siberian tiger. Likewise, Leo comes from Panthera Leo, the genus that lions belong to, while Tusk most likely comes from Tusker Elephant.
On the other hand, the Deathgaliens are based on minerals (galian is the Malaysian word for mineral). Ginis could be from the Japanese word for silver (gin) though his main motif is gold. Azald comes from the mineral azurite, Cubal comes from cubanite, and Nalia is most likely based off of jalpaite. Even Jagged resembles stibnite.