What's the Name of That Book??? discussion

I read a book within the last 2 or so years with a sword on the cover. I believe it was co-authored and involves a number in the title. The gist of the story/plot is that there are a certain number of relics being guarded by elderly people who start being killed off. Nephew of one of the guardians is the main character. Trying to find similar reads and of course cannot remember the title. Thanks in advance.

Six Heirs by Pierre Grimbert maybe?

Many years ago a few people were shown something secret. Their descendants meet up every few years in a big gathering and pass the secret along to the younger generation. This year the members are being killed off.

No, thats not it but it sounds very interesting and now I will likely read it - thank you!

Finally had a spare minute from my baby to check the bookshelf. Title is Thirteen Hallows.