To this date I have never seen a legitimate reason to submit false information to the United States. The honest response is what you just said, that because you are married your parents aren't going to be supporting you financially. Based on what you said, when he applies, having a married sister wont prevent him from going to school.
It is important that all answers in USCIS /DOS applications be answered accurately and honestly because the document has to be signed with the statement such has been provided truthfully. It is better to state the truth and explain it out than not state and be presumed to have lied to obtain immigration benefits.
Legal disclaimer: The statement above is provided by CC Abbott is based on general assistance and not intended to be a legal opinion because not all the facts are provided. The person requesting information and all others reading the answer should retain an attorney who is permitted by the state bar within the jurisdiction who can examine the complete facts and provide a legal opinion on your case. All information provided in the above answer and other information provided by CC Abbott does not create an attorney/client relationship within any state of Federal law.
Your brother needs to be truthful in answering the questions on the visa application.
J Charles Ferrari Eng & Nishimura 213.622.2255 The statement above is general in nature, as not all the facts are known. You should retain an attorney to review all the facts specific to your case in order to receive advise specific to your case. The statement above does not create an attorney/client relationship.