My sister says she has small bowel lymphoma. are family members more likely to get the same thing?

Not likely: Vast majority of the cancers, including lymphomas, are sporadic. Unless there is history of multiple family members, in earlier generations, having small bowel lymphoma, your family members are not appreciably more likely to develop the disease.

No: Genetic causes for lymphoma are rare. There are small demographic groups were certain types of solid cancers are more common. These cohorts of patients are small.