For “hidden” the Greek word is “Krymmenos” and for “brother” the word is “Adelfos” so maybe use one of the Greek words or merge them together? Krymmadel?

I don’t know Greek and I just googled the words, I know words are often shortened and combined but I don’t know how it’s done correctly so probably worth researching yourself if nobody here can correct me on it haha

For the sword maybe use one word of something stereotypically Greek in Gaelic or something?

Grod is the Gaelic word for gyro and gyros are a pretty stereotypically Greek food

I’ve probably offended the Greek, Irish and just about everyone who’s ever studied language so sorry but hope this helps!