We use the Dordt Church Order as well and translated it int German here: http://www.serk-heidelberg.de/uber-uns/kirchenordnung/
I know what it says, but there are some practical questions that are not addressed by the CO. Also, I don't think it explains whether pastors are members of classis (which they are in Presbyterian circles, but would be hard to do in Dutch circles, as classis is no permanent body, right?) or of the local congregation.
You are right, it only mentions that the elders are members of the local consistory (art. 37), not if they are also members of the congregation. They are however, as any 'normal' person, member of the church, so they belong to the congregation. They, and their families recieve 'normal' care from the elders (and deacons): they visit the families of the pastors on a regular basis, as they do visit everyone else.
The classis is no permanent body indeed. Local churches send their pastors (or one of the pastors if there are more than one) to the classes and one elder per church. And the classis sends to the particuliere synode, the particuliere synode to the generale synode.
PS: I am a member of the Reformed Churches in the Netherlands (liberated) so i am a little bit a stranger on this forum