this.j isn't accessible to the child in the parent object, change your variables to temp ones and you'll be able to access them.
PHP Code:
new GuiControl("container") {
this.j = 5;
temp.k = 6;
new GuiButtonCtrl("button") {
echo(this.name); // echos "button"
echo(this.j + 1); // echos 1
echo(parent.j); // echos 5
echo(temp.k); // echos 6
}
}