You may be able to clean up the signal using a Compressor as used in the recording industry..Beringher make is cheap and good quality or others in the 19 inch rackmount format can be found on auction sites s/h around 20 pounds sometimes...this is without knowing what you've tried already of course and no guarantees..but the signal sounds like it needs the opposite of any process that gave stretch and warp...i.e compress
If you can't, turn the sound off and add a newly recorded soundrack of your vocals and use someone else for the other people etc. Just chop the new sound into bits on computer to make the mouth movements suit. More work but doesn't cost anything but a mates time etc.
Or put text on it.
Other than that get a magazine at tesco or asda/whs etc with a free soundlab editor programme. Will take some practice and time though.