The card chosen to represent the situation is the Ace of Swords. This card symbolizes the beginning of a new cycle, so it is possible that you are preparing to start a new phase in your relationship with your brother/sister. The Ace of Swords can also indicate wishes for success, motivation and determination. These characteristics may be needed to face a challenge in the relationship between you and your brother/sister.
The card chosen to represent the challenge is the Three of Swords. This card represents something difficult to overcome such as a problem or worries. There may be circumstances that cause tension and discomfort in your relationship with your brother/sister. The Three of Swords can also indicate a need to be honest and tell the truth about something, so the more difficult issues between the two of you may need to be addressed.
In conclusion, it seems that you can expect a discussion with your brother/sister to address the circumstances that have created tension and discomfort between the two of you. The cards suggest that it will be necessary to be honest and tell the truth about something to solve problems. So the answer to the question is, "An argument awaits me."