Thank you for writing.
The items in the layout control do not have AutoSize functionality. In fact, what you need should be achieved, by controlling the item height, which will size the grid, not the other way around.
The group item hosts LayoutControlItem and you can set its MinSize/MaxSize properties to control its size. Once the item size is changed, it will change the inner grid size as well:
Please give this approach a try and let me know how it works for you.