The autoResize attribute of group nodes determines the resizing behavior of group nodes while interactively moving their child nodes.
It is not possible to prevent the hierarchic layout algorithm from resizing group nodes.
Unfortunately, this is not possible in yEd.
However, the yFiles diagramming library (upon which yEd is built) does offer the possibility to enforce specific orderings for (normal) nodes and minimum sizes for group nodes.
So, if you are a software developer, it might be worth your while to take a look at yFiles.