if marriage looks good like first background checks are fine, no divorces, no criminal record, no USCIS previous record, then 99% times they do initial interview just to see a couple confirm all stated document, ask all those "No" questions like are you terrorist, are you in fraud, etc, etc, and they collect evidence. if this is enough, you got GC 2 yr then you are RFE and get 10yrs if the story make sense. If something stinks they call for so called "follow-up interview" but in fact it is "fraud-department interview", if they call for 2nd interview they have serious reasons to believe it is a sham, since it is expensive to set up interview (the office take time, plus each USCIS office has to fall under some % of follow-up interviews, not more than that), second interview is 99% separate, computer generate bunch of questions, you get one person answer them while spouse waits outside, then the same questions to second person. thats all it is still very official and simple, then they take your answers next to your spouse and look how much of a difference and make a decision accordingly.
if a marriage is entered into a good faith, couple does not have any criminal record, no uscis records no divorces, etc, it is a waste of money to take attorney on the first interview. if there is any shame on file, I would take attorney just in case. attorney does not have a right to talk during the interview, but if the case is fishy and you have gone through alot with USCIS so far, it is good to have attorney just as a witness, if later you are denied and appeal attorney can testify what was said or not said, also attorney may say that OP is pushing too harsh, but not likely this happens since OP will not ask nasty or dirty questions IF attorney is present.
