If your group is public, then all web maps shared to it need to be public as well in order to be seen in the gallery. If your group is private, then you would be prompted to sign in first, which would then allow you to see the web maps shared just to the group.
As far as ordering what you see in the gallery, you can control sorting from the item in your My Content that represents the map gallery. Look for the Configure App button. This provides some control over the sorting order. You can sort by date, ascending or descending, for example.
Thanks,
Mike