You seem to be able to use words fairly well, so your letter should sound intelligent in that area. You should point out his good characteristics, be detailed and use examples to show what you mean when you say he is a good person. You also mention his hard life. Give examples of this. Try to demonstrate that he has changed since his arrest. Talk about hings he might have said or done to show his remorse. At the end, try to convince the judge that your new family will be a major factor in changing his behavior. He should agree with everything you say, chances are, the judge will ask him about the things you say.