Visit visa requirments from Pakistan

Hi Gurus, Hope any of you can help me with following question Thanks in Advance.. I recently Graduated from Oxford Brookes University and my graduation ceremony in End of June.. I want my parents to attend graduation.. University have send me letter that i can request them to issue sponsor letter or i dont knw wjatever it call they can isdue me.,, My visa was refused and i am still
in appeal process i really dont know how long will it take..Do i hve to have visa to sponsor someone?? What other requiments?? Can i send them Uni letter and they can show thier bank statments will they able to get visa? What are the chances?? Plz answer asap.. Thnks

Your parents can apply as general visitors without your sponsorship, so your presence in the UK is not relevant to that type of application. You would not be a sponsor of their application unless you were providing some resource that they could not afford for themselves.

Thank you very much for your reply...Will this letter from UNI is going to help or not???

Not really

What is the general visitor requirments??how much bank stmnt they need the hve already been here once but got sponsor off from smewhere and cant get sponsor nw..