Yes, the phrase "Seriously venting to my brother" is grammatically correct. It means that the speaker is expressing their emotions or frustrations in a serious and possibly intense manner to their brother. "Venting" typically implies talking about issues, emotions, or frustrations to relieve stress.
You can rephrase it in several ways, such as:
- "Having a serious conversation with my brother about my feelings"
- "Expressing my frustrations to