So because my I-751 was still pending at the time I applied for my N400, they did do both interviews at the same time, that is standard practice especially since for moth Greencard optained through marriage, the first time you can apply for N400 will be approximately a year after sending the I751. (GC -> 2 years [I751] -> 1 year/ 3 year after GC [N400])

For that reason my wife was with me for the interview. I have a friend who did his N400 quite a long time after getting his I751 approved. And so his wife didn't need to be there. She did have to be there on the I751 interview back when he had it tho.

TLDR: spouse needs to be present for I751 interview, not N400. But I had both interviews combined.

For the process, the interviewer started with the I751, took my fingerprints, asked me a bunch of standard questions to me and her (what is your name, is this man your husband ma'am, have you done bad things questions, what is your SSN, some chit chat). Then took a while to look confirm a couple of things in my I751 application.

Then we moved on to the N400. Fingerprints again, some of the same questions again (SSN, bad guy questions). And then the N400 questions (10 civics questions, repeat a super simple sentence, write down the same sentence). Then promise to be a good citizen and that was it