We are a long way from understanding and explaining pain. How pain gets started and why it doesn't go away for some people is a key area of research.
Studies clearly show that most people report pain in more than one area at a time. Some pain patterns are almost predictable. For example, back pain is more likely to occur in people who also have facial pain. Back and knee pain together are common.
Is this because back and knee pain are the most likely places to have pain in the first place? Is it just by chance that they happen at the same time? Or is there some pain mechanism that turns pain on in paired locations?
None of these questions have answers just yet. Risk factors (including heredity) are being studied. Since the occurrence of pain at multiple sites affects so many people in the general public, heredity isn't strongly suspected.
Other risk factors such as occupational activity may be a more likely cause. Repetitive motions involving the entire body may lead to pain in multiple sites. Certain conditions such as fibromyalgia or osteoarthritis tend to affect more than one area at a time.
Social, cultural, and economic risk factors may have a distinct role in type, location, and severity of painful symptoms. Since family members tend to share these characteristics, they may be the reason why you see similar pain patterns among your relatives.