you are not giving any details whether you use the Composition Editor, WindowBuilder or if you are down at the ExtendedWidgets level by hand-coding (which I guess you are not).
As a first answer: there are solutions for your problems in all three, but none of them are extremely easy and involve some hand-written code. But still the good news is: What you want to do can be done. WidgetKit from Instantiations offers some support for what you need, you should probably take a look at that.
As a side note:
The whole Grid/Container Details/Container Icon Tree stuff in VA Smalltalk is overdue for reengineering for many years now (it has been in the IBM era), and I know Instantiations is well aware of that. But as far as I know there is no concrete announcement of such a new version of the GUI controls. There are, however, announcements on GUI improvements for the next releases, which, to my knowledge, does not include the upcoming 8.0.3 version of VAST.
If VAST 7.5 is a fixed requirement for you, you have the choice of looking into WidgetKit/Controls or learning how to hand-code stuff.