I'm not a doctoral candidate, but I can't possibly see how this would be good. Is there a shortage of qualified advisors?
Qualified advisors are plentiful, but are there formal or informal rules that govern the selection of committee members?
I don't find anything in the UF catalog, graduate student handbook, or my departmental manual saying a relative can't be on your committee. That being said, I probably would not have a relative as the committee chair.
rule or not, consider how this would be perceived five years from now, ten years from now, or twenty years from now when someone whispers in the halls that so and so on your dissertation committee was a relative. BAD IDEA. And I would look askance at any institution that allowed it without a THOROUGH examination that found that no other qualified person was available.