The commandment to love and care for others, perhaps the most important in the entire Torah, while applicable to all is phrased in the context of one’s friend or neighbour. It is actually much harder to love a neighbour than a stranger. With the latter we have no complaints over loud noise from a barbeque party, overhanging trees and blocked driveways. 
Most of us like people in general, it’s just that when we actually interact with them that we notice their faults and may get into the occasional argument. 
If the Torah exhorts us to specifically love those who are near to us we can readily understand how our Sages understood the command to “love your neighbour as yourself” as a reference to our spouse (Kiddushin 41a). They are truly our closest neighbours and it is to them we must show our greatest love[1]
Yet the greater the potential for love the greater the potential for hatred and as any family lawyer can tell you there are few hatreds as intense as those resulting from a bitter divorce. It is a sad reality that intense love can turn to intense hate, perhaps the key factor of the current day agunah crisis where the get is used a bargaining chip and worse. 
It is this potential of hating those closest to us which may help explain what is at first glance a rather startling Mishna that teaches “even those who are not believed to say your husband has died may bring a get (Gittin 23b).”
As we discussed when we learned masechet Yevamot (see here for example) Jewish law allows a woman to remarry based on the testimony of one witness, “[in order to prevent one from becoming an] agunah the rabbis were lenient (Yevamot 88a).” This leniency was extended even to those generally disqualified from testifying in a Jewish court of law such as minors, non-Jews and relatives. Though the testimony of most relatives - a cousin, uncle or aunt, parent or child - is accepted the Mishna lists five relatives whose testimony that a husband has died is not accepted and the wife may not remarry.  
These five often harbor hatred towards the wife despite or shall we say because of their close relationship. I must admit I have always found this Mishna difficult to comprehend. It is family members who care the most for each other and I would have argued that their testimony is the first to be believed. Yet while they may love them more than others, our Sages were acutely aware that it is those whom we love the most who we often hurt the most[2]
Such hatred does not preclude love and a sense of family loyalty - it’s just that both can actually co-exist. And the Sages feared that the “hatred” may manifest itself when testifying about the fate of her husband. By falsely testifying that her husband has died the wife who remarries would be forbidden to return to her first husband when the “lie” is exposed, thus effectively driving the woman out of the family. 
Little explanation is needed as to why one co-wife may hate the other co-wife and would be happy to see her marry inappropriately thereby leaving the husband for herself. Even the closest of actual sisters, and few were closer than Leah and Rachel, were torn apart once they had to share a husband, a dispute that carried over to the children with tragic consequences. 
The Mishna also disqualifies a mother in law from giving testimony that would allow her daughter-in-law to marry. The at times fierce resentment and even disdain for a daughter-in-law (or towards a mother-in-law for that matter) is not something unique to our generation. Not only is a mother-in-law disqualified from giving testimony but so is her daughter i.e. the wife’s sister in law, her husband’s sister. 
The Gemara explains that the resentment towards her sister in law stems from the fact that the inheritance from her father will end up in her sister-in-law’s hands. This due to the fact that in theory[3] only a son, but not a daughter, inherits with the son being responsible to support his wife and his sisters. The upshot of this is that a man’s daughter-in-law will end up with his wealth with the daughter herself receiving only that which her husband may have. 
The other two women who may harbor ill will towards the wife are her “other” sister in law, the one married to her husband’s brother. This is so because should her husband or brother-in-law die due to the laws of yibum she will become a co-wife with her sister in law. The last of the five relatives barred from giving testimony is the husband’s daughter i.e. the wife’s stepdaughter. Blended families can be messy and we have no assurance that the stepdaughter has her stepmother’s best interests at heart when she testifies.
While these five are disqualified from giving testimony as to the status of the wife they may deliver a get to the woman. In this case we are not relying so much on her testimony as we are on the written text of the get. And we do not suspect that these women may forge a get to mess up the wife. It is those lacking competence as in a cheresh and shoteh, a deaf-mute (of Talmudic times) and a fool, or a minor who are disqualified from delivering a get. As we discussed in our last post they may be able to write the get but they cannot deliver it. 
The Mishna lists two additional groups of people who while they may write a get cannot deliver one; a non-Jew and the blind. The former as the Jewish laws of marriage and divorce have no application to them (as to why they can write a get please see our last post). Regarding the blind the Gemara explains that it is only gittin brought from outside the land of Israel where the agent must declare “before me it was written and before me it was signed” that a blind person cannot do so. Gittin written and delivered in the land of Israel where no such declaration is necessary may be brought by the blind. As to how they can identify from whom they received it and to whom they are delivering it the Gemara explains that they do so through voice recognition. Fascinatingly the Gemara derives this from the fact that just as we can rely on voice recognition to permit a blind person to be intimate with their spouse so too we rely on such recognition in the identifying who is giving and receiving the  get. Speech can bring people together or can tear them apart - it’s all in the tone we use. 
[1] On a practical level there are few people besides a spouse who we can love as ourselves. Even our children we cannot truly love as ourselves - only more than ourselves.
[2] While this is not how the Mishna is generally understood lulei demestifina, (a beautiful rabbinic idiom which literally means “if I were not afraid” but in practice means I really want to claim this but won’t because great rabbis have rejected this view) I might have argued that for some of the disqualified relatives it is precisely because of their great love of their relative that they may jump to false conclusions so that they not be rendered an agunah. For some, like a mother-in-law in law, some love their daughter-in-law as a daughter and some have opposite feelings.  
[3] In practice it is recommended that legal loopholes be used so that we may leave equal inheritances to both sons and daughters.