I just noticed that the tiledbackground object not show up in the family list. Is it a bug or its impossible to put them into the family with other sprite objects family?
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families are object specific. You can have sprite family, tiledBG family... but you can't mix different objects in one family
See Families in the manual. A family must consist of all of the same kind of object (e.g. all sprites, all tiled background, etc.). So you can create a family of tiled backgrounds, as long as all the other objects in the family are tiled backgrounds.