Is there a way to get any offspring that belongs in a certain group directly?

Question

You can get all members of a group:

get_tree().get_nodes_in_group("group")

You can get all children:

get_children()

Is there a way to simply get specifically children that are in that group?
Is the only solution to get all children and then filter by their group?

Answer 1

I don't think there any single, built-in way to do that. I'd probably get the nodes in the group of interest and then get their children. So, something like this:

func _ready():
    for node in get_tree().get_nodes_in_group("the_group"):
        print(node.name)
        for child in node.get_children():
            print("   " + child.name)

Answer 2

Is the only solution to get all children and then filter by their group?

Yeah, or the other way around:

var children_in_group = []
for node in get_tree().get_nodes_in_group("the_group"):
    if is_a_parent_of(node):
        children_in_group.add(node)