The appropriateness of kissing siblings on the lips can vary based on cultural norms and personal preferences. In some cultures and families, it is considered a common and innocent display of affection, while in others, it may be seen as inappropriate or uncomfortable.
In many Western cultures, kissing siblings on the lips is less common and may be considered unusual or awkward as children grow older. As siblings reach adolescence and adulthood, it is generally more common to express affection through hugs, cheek kisses, or other non-lip contact.
Ultimately, what is appropriate is subjective and can vary from family to family. It's essential to respect each individual's comfort level and boundaries. If you or your siblings feel uncomfortable with this type of affection, it's perfectly acceptable to communicate your preferences and find alternative ways to show affection that make everyone involved feel respected and at ease.