Why write a judge before sentencing court date for family member?

Because often, when handing down sentences, judges take into consideration what's called mitigating circumstances. Mitigating circumstances are things which may reduce the family member's sentence. Examples of mitigating circumstances are abuse as a child which may have lead the family member astray, substance abuse that made him or her act different than he or she normally would and more importantly, other good deeds that the family member has done, such as provided for his or her children, been a great parent, done charity work, helped people, etc. If you can show that, even in spite of the crime for which the family member has been convicted, that the family member is still a contributing member of society, the judge may be more lenient with the sentencing. And although family members of the convicted person may have an opportunity to testify to these things at a sentencing hearing, putting information in writing for a judge to receive in advance of the sentencing hearing and put in the record is always a good idea because, for the most part, things are given more weight in the legal world when they're in writing. What's more, the earlier this information is received by a judge, the better. It'll stick in his mind as a part of the court record, rather than testimony that he heard minutes earlier which is more likely to be overlooked.