What format are the DVD files?
Assuming also that the DVD is not scratched or flawed(?)
What brand and type of media were the (assume camcorder) data burned on to?
Were the disks provided by a professional photographer? Could be that there were intentionally included structural errors that prevent copying so you have to buy copies from him/her.
Try using AnyDVD's "Rip to HDD" feature. That way your wedding disk data will pass through the "FixVTS" feature and may get the data to your HDD. Once accomplished you should be able to use most any backup software to copy it.
BTW: anything good on this honeymoon DVD?