I don't know your whole story, but I am sorry you are going through this on top of health problems. Do you have any friends or family members that will testify on your behalf as to how vindictive the inlaws are being. They could always write letters to the judge and offer to be interviewed. I really don't understand what any emails from 10 years ago should apply to today's case. In a world where so many children are abused or in foster care because of an adults actions, I would hope that the court would leave you alone since you have proof that he is being loved not harmed.
Best of luck.