1. Yes, your drivers are not really self-employed if they are driving your vans. Leasing the vans to them is an option. That would then make them self employed with outgoings and income. However, again I would suggest that whilst you can maintain a group cover policy, some element of payment should be written down for the insurance as well. Otherwise, the Revenue might query this arrangement.
So what contracts do I need? I do understand that I need to invoice them for the van and insurance.
2. Yes, you should get a rental contract for the van, which also deals with the insurance element. Your local solicitor should be able to help you with that.