Table bed cushion problem

My solution involves modification of the table and replacing the useless cushions with ones I made. I just finished a write-up in my mods (see link in signature). Other than that, you could try sewing hook and loop (such as Velcro) to the parts of the cushions that are up against the others to help hold them together or use the shelf-lining that looks like a screen that is non-skid to help keep them from sliding so easily.