You need to take time for yourself. Maybe a brief written letter to your aunt and your mother, and then don't worry about it. Explain that they have made their choice, and if they cannot mend their differences, you cannot do it for them. They both need to - pardon the expression - grow up. Their daddy isn't around to stop them squabbling, and it is not your fault.

In fact, not only should you not feel guilty, you should make it a rule that either of them can contact you, but you aill hang up the phone if either brings up the feud, or each other. Declare yourself a neutral zone. You'll sleep better!

(This is what my Dad did with one set of his relatives when I was a kid. It was their loss (those who wanted to continue a feud at all costs), and not his at all. He feels that way to this day.)