Family history is not always the best predictor
Siblings are important when it comes to risk factors; brothers and sisters of those with the cancer have a higher risk, and an especially high risk if they are an identical twin. However, most people who do have Hodgkin lymphoma do not have it in their family history. Therefore, there is little clarity regarding the risk of family history in general. Some assume the connection between siblings, but not their parents or grandparents, is due to similar childhood exposures to infections like Epstein-Barr Virus.
Those who have HIV have a heightened risk of developing Hodgkin lymphoma as well.