Ha, yeah. They don't make it super easy to sort out, especially with the constant loading.
Basically, if you click "List of Locked Souls" at the top you can go over to the "Legendary" tab and pick out which one you're going to start planning toward. When you click on that one, you can see in the bottom-right where it says "You Own/Req Points/Soul Req. 1/ Soul Req. 1", and those last two will show you which two Elite souls you need to level to unlock them. Then you go to the Elite tab and do the same to see which two Standard souls you need to level up to unlock those.