Since you are asking about removal of conditions, this means you already had an interview and were granted conditional residency. The issue now will be whether the conditions can be removed; if you have questions about the evidence is to be considered now consult an excellent immigration attorney; you will need to update all your proof of good faith bona fide marriage and USCIS can ask any questions relating to your relationship; good luck
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"Before marriage" is not necessary, but cannot hurt if you have such evidence. The documentary evidence you need to submit to remove conditions is your lives together as a married couple, from the day you got married, to this very day when you file the I-751. The type of evidence to be submitted is the same as the what you brought to your first green card interview, (you need to submit that all over again) only now it needs to be brought to date, with any new type of documentary evidence added to it such as the birth certificate of a child born to the marriage, etc. (the list of most of the documentation to be submitted worth your I-751 can be found on your old I-495 interview notice you received from USICS, use it as a guide.). You will also need 2-3 notarized signature letters from your mother in law, and your USC spouse's friends attesting to the genuineness of your marriage.
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Evidence of your good faith marriage should be submitted with your I-751. Some good examples of things you can submit have been mentioned. You want to submit as much as possible in your packet. Evidence prior to the marriage can also be submitted, but should not be a substitute for the prior two years since the conditional green card was submitted. If you have been scheduled for an interview, I would highly suggest consulting with an attorney, as the good faith marriage may be in question.
At what stage are you? It depends on your circumstances. If you want peace of mind, go to a quick consultation with an attorney or take an attorney with you to the intervuiew just to make sure you are doing the best for your case.
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