Getting married is a major event in life, not to mention your sister's wedding. It is true that family members do not need to give gifts, and you may even have to help collect money. However, as a blessing, you should give your sister a small gift. Here are some suggestions:
First, give a child bucket, a good wish for marriage and childbirth, and also wish your sister's family prosperity, happiness and harmony. I believe that your sister and brother-in-law will like it very much.
Second, give a gift that your sister likes. I believe that after being together for so long, you should still know your sister very well. Giving her a gift she likes can also be regarded as a role model for her brother-in-law!
Third, give a creative gift. You can make a family portrait of a real-life doll of your family. Of course, you should make your brother-in-law one. If you put it in your sister's home, she will often see you and your parents, and it can also show that there is a harmonious atmosphere at home. They must like such a wedding gift very much.