[Thamnophis]

You have to know which organisation(-s) you get to deal with in the state where you export the snakes from. But also you will have to contact the airline with which you will fly. And you will have to with which organistation(-s) in Holland you have to deal with.
Try to get information on paper with all their demands and costs etc.
And then you start organising everything.
I have no experience with this, so I know nothing for sure.