This is a very interesting complaint, but it is difficult to know too much about what is going on from the information that you've provided so far. How long has this been going on for? Are there any other symptoms? Is there any bruising, discoloration, changes in your hair, or anything else that is going on in this area? Do you and your family members all do your hair in the same fashion?
As far as medical reasons that all of you are having this tenderness in the same area, it is likely that there is something that all of you are doing, perhaps with regards to how you wear your hair or how you sleep, rather than that all of you have a particular skin or scalp condition that would cause tenderness in this area. The caveat, of course, is that if you are experiencing pain that lasts for longer than a couple of days, is associated with other symptoms, or is worrisome in any other manner, you should speak to a physician who can actually look at the area that is affecting you and give you some more information about what could be happening. Some possible things that could be causing this tenderness would include how tight you are pulling your hair back up, and any things that you might wear in your hair. Infectious causes of skin or hair pain would be another thought, but it would be less likely to affect all of you in the exact same way. Please see a doctor
for more help with this question.