Yes, you may bring a US immigration lawyer to the green card marriage interview. However, your immigration lawyer cannot answer the questions for you or your spouse. Your immigration lawyer will probably increase your confidence, legally supervise the interview and protect your legal rights during the interview. Also, if for example, the USCIS Adjudicator requests a document from your file your immigration lawyer will normally find it faster than you and may provide a legal explanation for its absence. If you hire an immigration lawyer to come with you to the green card interview, you should ask him or her to study your file beforehand and make sure that you have everything you need, including updated financial documents for the affidavit of support and criminal disposition of arrests or criminal cases you may had in the past.