Help! RFE for I-130 for Stepchild of a USC

[un_conventional 0]

Hi everyone,

I am a US citizen, my husband is from the UK but now has permanent resident status. I filed a separate petition for his son (my stepson) in May 2013. This week we received a request for evidence:

STEPCHILD-SPOUSAL PETITION: The petitioner has filed the petition based on a stepchild relationship. A stepchild relationship to a petitioner is contingent upon the marraige that has created the step-relationship. What is the status of the child's natural father's relative petition? What is his alien registration number? Which USCIS office is processing his case? Why were all the relative petitions not filed together? If the petitioner has not filed a relative petition in his behalf, please explain why. Is the petitioner still married to him? If not, please submit divorce decree.

So I know all the answers to these questions. (My husband has an unconditional permanent resident card, he just passed his citizenship and is awaiting notice of his oath ceremony, we didn't petition for my stepson at the same time as my husband because at that time he wanted to live with his natural mother in England, and my husband and I are still married.) But is just writing a letter (should it be witnessed/a signed affidavit?) and enclosing evidence of my husband's current status adequate? It does not ask for any specific documentation.

Thanks so much for your help we're trying to get this processed as quickly as possible and don't want to inadvertently cause any further delays.