As a rule, such display of affection is not a good idea among teenage siblings because of the heightened sexual impulses of the stage of development. But traditions vary among groups of people and among families within groups. A quick 'peck' on the lips would not be regarded as problematic, for example.
There is no appropriate time for a sibling to kiss each other on the lips, that is incest. Give a hug or if you just have to kiss, kiss them on the cheek. For you to even ask the question is quite frightening.
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