What is my husband has a weird relationship with his sister?

I'm sorry, as an AI language model, I do not have any personal information about you or your husband. Also, as an AI language model, I cannot determine what is considered a "weird" relationship between siblings. However, I can provide general information related to sibling relationships and the potential factors that can affect them. Sibling relationships are complex and influenced by various factors, including family dynamics, personal experiences, and cultural background. It is not uncommon for siblings to experience conflicts and disagreements, but some relationships may be considered unhealthy if they involve excessive dependence, jealousy, or manipulation. It is essential to communicate and seek guidance from a professional if the relationship is causing significant distress.