Eli is a nickname, a shorter version of the name Elijah.
Sometimes, people who are close to others will give them a nickname, pet name, or rabbit name (however you want to call it) that is either a fun, loving representation of that person, or is actually a shorter version of their name.
Like my oldest daughter is Samara, but we've shorten her name to Mara for when we're just quickly calling her.
She's also Samo, a nickname given to her by her best friends of eight years.
Her grandma and cousins call her Munchie, or Mouse, due to a silly thing she use to do when she was a toddler.
To her writing friends, her username is DragonPhi - based off of my username.
And I call her Kat, cause we illustrate a little comic for our city newspaper called Kitty and Kat - I'm Kitty. We've been doing it for so long, we're use to calling each other that when we're being silly.
So, this is just a really, really deep explanation and example of what's going on in the RP here.
Kris is just use to calling Elijah - Eli. I figured that, when he was younger, he couldn't say Elijah well. So, he just called him Eli. Caden would have probably been called Cady, and Jareth was probably Jarit... (thinking like a two year old here). But, Cady and Jarit would get him killed now. But Eli stuck with him, and probably with the rest of the brothers as well. It's just easier to say - and type. LOL!
I hope this helps you, but if it's easier, I'll just change it; it's not a problem.