"You believe in yourselves."
Translation:Εσείς πιστεύετε στους εαυτούς σας.
τους εαυτούς is accusative case
οι εαυτοί is nominative case. I'm not sure when you would want to use it, since nominative case is mostly used for the subject, and reflexive pronouns refer back to the subject -- so they can't really be the subject themselves. "Ourselves took this picture" ??