The zodiac sign is called Gemini because the Latin word for "twins" is "gemini" (singular "gemina"). It's also why the linguistic term for pronouncing a sound twice as long is called "gemination" (and in dentistry, a double tooth is called a geminate tooth).
Yeah. It's (predictably) similar to the word for 'twin' in a lot of Romance languages.
Why is "filoj"not children? Twins can be both male and female and gender is not presumed by "filoj" right?
I think "filo" is specifically "son". "Offspring" would be "ido", "child" would be "infano".
Here's what I have so far:
ge- = both sexes
in- = female
bo- = in law
pra- = great
gxe = twin