Yeah tons of my girl friends call me jaan too. It’s a term of endearment…
Then again, you are certain that both of the texters are boys, in which case, it does seem like she is leading both boys on.
I know its bugging you because she seems two-faced, she maintains an innocent exterior but privately she has the sort of relationships where boys call her “jaan” and express how “important” she is in their life. That’s not so innocent.
Why not distance yourself from this friend since you are able to see that she is not who she advertises to be? Do you really need to be around someone like her? And don’t bother alerting your male friends, they will see you as meddling. Furthermore, they still think she is a sweet, innocent angel and will start to see you as the bad guy for interfering and sullying her reputation.