Dickinson, who is 22, has made 60 appearances for City and has had temporary spells at Blackpool and Leeds while 20-year-old Shotton has previously been loaned to Altrincham and Tranmere.
Fikelovic initially arrived at the Championship side on trial under former Tykes boss Simon Davey.
"He is an international defender who will bring stature and experience to our squad," said manager Mark Robins.
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