CMJAIN.
Answer is very simple: you have a "one time use weapon" in your hand. Either use it for fighting maintenance case or against your FIL proving that its fake.
Also remember things for using against out-laws-
- Burden lies on you to prove that its fake
- Analyze what maximuim punishment your FIL can get even its proved fake and compare, Is it worth destroying income/experience proof of wife?
- They may have also have done some manupulation at school records to show its true, knowing the fact you can use this letter against them
Regards
