In regards to the paving sand, it's natural that it will get washed away when you use the pressure washer. I recommend putting in a fresh batch of Dingo 20kg Powerloc Paving Sand. This will fill in the gaps between your pavers and prevent them from moving.
Here is a handy step-by-step guide: How to pave a pathway (the last portion of this guide is the spreading of the paving sand and how to apply it)
Please keep us updated with your progress, we look forward to seeing your pavers rejuvenated.