Something similar to this happened to my great grandmother. Her older sister died in childbirth with her second son. It was just expected in her travelling community that my great grandmother would marry her brother in law although she recalls she was just 15 at the time.
Having seen her sister die a very painful death, my gran was not keen to get married or have sex, but she was given no choice in the matter.
Her brother in law/ husband was a violent man. Fortunately for my gran, he died a few years later, and she courageously broke away from her community and started a new life with her two daughters and two nephews.
Obviously I'm not suggesting this tradition is still commonplace in travelling communities. However rates of domestic abuse are still frighteningly high and I'm grateful my gran was able to get her family away from such a toxic environment. Her nephews grew up to be lovely, kind men.