Nice study, although I don't believe there is a correlation. Such an idea could only grow over time I guess, e.g. both my parents and all siblings are introverted.
Me (being the oldest): INTP
Brother ISTP (probably)
If I may have one request, could you find out if it is common for a single MBTI type to occur more than twice within one family (parents + children)? My hypothesis would be that it isn't.