FYI since the laws in Europe are most likely similar to the laws of Canada on this, it can get your "contractors" into big trouble with their tax agency.

I know a lot of people do that (work as contractor but they are employees), but if you bother to read the tax code this is illegal. It takes one audit to be reclassfied and then you have to repay the taxes your employer would have paid. This can be retroactive for many years after employement has ended.

Stay away from those contracts.