If you can look 10 billion light years in one direction, and 10 billion in the other, and the Universe is SUPPOSEDLY only 15 billion years old, then the two galaxies at either end would have still been 5 billion light years apart when the Big Bang supposedly went off.
Got it?
Umm, you're neglecting the important point that both galaxies are moving away from the focal point in opposite directions. There's no discrepancy there. In 10 billion years, they can get 20 billion light years apart (travelling at the speed of light), since each travelled 10 billion LY from the focus.