I didn't know that gall wasps could parasitize other gall wasps.

Cynipidae is divided into two subfamilies: Cynipinae, the gallmakers, and Synerginae, which are inquilines in the galls of cynipines. I imagine it's possible to tell the two apart from photos like this, if we could only find someone who knows something about cynipids.

it's worth while to have the Cynipids divided into the subfamilies?

It looks like the key to separating the subfamilies is getting good shots of the abdomen. This is how they are distinguished in Ashmead 1903:*

Synerginae: Second segment in female very large, occupying the whole or nearly the whole surface of abdomen, very rarely showing an indistinct dividing suture; if this suture is distinct or complete it is very oblique and the segment dorsally is fully two thirds the length of the abdomen; males with the second and third segments nearly equal, but here two segments occupy most of the surface of the abdomen; venter more or less covered basally.

Cynipinae: Second segment in female much shorter, but the longest segment; the second and third together not occupying two thirds the whole surface or rarely; venter always visible.

* Ashmead, William H. 1903. Classification of the Gall-Wasps and the Parasitic Cynipoids, or the Superfamily Cynipoidea III. Psyche 10(324):140-155.

That doesn't sound very easy to get those shots on live wasps. The wings always seem to be in the way.

This one of yours shows the abdomen perfectly:

I guess we need to try for clear lateral shots. If I'm interpreting the descriptions right, that one and the three below are cynipines:

and these would be synergines:

I'll try to get confirmation before I go moving images around.

I think it would be if we could find someone to start sorting out which is which. I did find one person who studies cynipids, who I was going to try contacting in the next couple of weeks. I'll see what he has to say.