The ceremony is to be held at the K Club in Co. Kildare, where there will be free alcohol on hand, and Peggy has warned the rockers they must be on their best behaviour.
A source told the Daily Star newspaper: ''Liam and Noel refused to go at first. They still don't want to see each other. But Peggy has insisted that they are both there. A few family members are expecting it to be very awkward. But Peggy has told them there is to be absolutely no drama or fighting on the day. She thinks they will surprise everyone though by sorting their issues out once and for all.''
Liam and Noel have barely spoken since their bust-up other than a few text messages exchanged and an surprise meeting at a post-Olympics party in 2012.
Liam's new girlfriend Debbie Gwyther was trying to encourage an Oasis reunion by getting the warring brother's older sibling Paul involved to persuade them to perform a series of gigs in 2014 to celebrate the 20th anniversary of their acclaimed debut album Definitely Maybe.
