Do I must send Affidavit letters for Form I-751 ?How to answer the PART 5.

It appears you are looking for help in filing your immigration paperwork, not divorce? If this is the case, you should post under a different topic, and try to include as much information as you can in your question.

Think of it as filling the glass of proof with water of evidence. You put too little - you are in trouble. But putting too much is perfectly ok. Having a child together is great, having all your financial lives together is a huge plus, and the third level is affidavits and pictures. Just make sure to follow the strict guidelines of requirements for affidavits otherwise they won't be admissible.

It is not required but can be helpful to establish good faith marriage.