You are only human and you can only divide your attention so much. Apologize for not being able to give them all attention and say that you have to tone things back a bit and take people in turns.

As others have said, do shopping out of sessions unless they just need one or two items. Agree on costs at least outside of session when everyone can do math right without getting information clutter. Use private IM windows in Skype to better organize matters. Make sure you have txt files on each character that you move details into.