alewis478b14_ESO wrote: »

I have 150 key fragments. I can open the vault, fragments are turned into 1 key, I loot a chest one time. Correct?

Correct, but as a heads up, and I'm not entirely sure it still does this as it's been quite some time since I've opened those and they may have changed it, but ALL fragments on your character are converted to keys for that vault. So if you had 600 and only wanted to use 2 keys, bank the other 300 before you enter.

alewis478b14_ESO wrote: »

I've also read that I should take friends and we each loot the chest and then can trade, increasing the odds of getting the piece you want. Does this also require those people to have 150 key fragments?

Unless someone else knows for sure, I thought that those were bound on pickup. I don't think they can be traded like normal chest drops in the dungeon. I could be wrong though.