As a brother, you can play many roles in your sister's wedding. What you do depends on your personal situation and ability. Here are some possible scenarios:

1.** Wedding planning assistance * *: It can help to plan the wedding, such as determining the venue, decoration, catering, music and so on.

2.** Accompany the groom * *: It can help the groom meet the guests, or accompany the groom during the ceremony.

3.** As a witness * *: If invited to be a witness, you can express your blessings to the couple on behalf of your family at the wedding and read the marriage certificate.

4.** Photography * *: If you are good at photography, you can be responsible for recording the wonderful moments at the wedding.

5.** Entertain guests * *: You can entertain guests at the banquet to ensure that they can enjoy delicious food and a good atmosphere.

6.** Gift money * *: As a brother, you may need to give some gift money to bless your sister's wedding.

Remember, the most important thing is to express your blessing and love for your sister and brother-in-law. No matter what you choose to do, you must participate wholeheartedly and leave a good memory for the newcomers.