Isn't it odd that the usual conflict of interest restrictions on corporate decision-making don't apply in voting situations? If we were hiring, and a candidate was a close relative of mine, I would be expected to recuse myself. However not only is it considered acceptable to vote in elections for a close relative, but even for oneself. Moreover, voters whose stand to benefit from a particular candidate's being elected—e.g., because that candidate promises a tax break to some class of which they are a member—are not expected to recuse themselves from the election.
I think some of these things can be justified. In hiring, the primary question isn't which candidate's hire would most benefit the individual members of the organization. Rather, the question is which which candidate would best further the mission of the organization. When significant private interests that are not aligned with the interests of the organization come into play, one's decision-making runs the danger of becoming skewed, and one may well need to recuse oneself. But it is not always necessary to recuse oneself when one has significant private interests when these interests are aligned with the goals of the organization. Thus, if I think a candidate would make a good research partner for me, and hence I have a significant interest in the candidate's being hired, this interest typically need not force a recusal (though one can imagine circumstances when it would). Now, in voting, one is making decisions for the good of the polis. But the good of the polis includes many of one's own goods. Therefore, many of one's own interests are automatically aligned in the interest of the community. It is in my interest to eat in order to preserve my life, and if I am a member of the community, then the preservation of my life is included in one of the primary goals of the community—the preservation of the lives of the members. However, if it is obvious to one that one's own interest conflicts with the on-balance interest of the community, recusal might still be appropriate, as far as this argument goes.
It may even be justifiable to vote for oneself. For, maybe, one isn't really voting for oneself, but for one's policies. And these policies one has, presumably, thought carefully through, and one did not adopt these policies because they were one's own, but because they seemed right. But this does not, I think, justify voting for close relatives other than oneself. For there, there is apt to be a bias which, paradoxically, may not be present in one's own case. While it at least borders on incoherence to adopt a position because it is one's own, it is easy and coherent (and sometimes rational) to adopt a position because it is that of someone close to us.