There was a thread about someone traveling with his son who could not check in because they had the same name. When one checked in it would check the other out. He ended up not being able to board and had to fly the next day.

My takeaway from that is to make sure the the names are different, not just in the middle name field. Mash the first and middle names together if you have to. Don't worry about TSA; they don't care. For a while a few years ago UA was appending "Mr' to one of my names when I booked through the app. I didn't have any problems.

The advice to make make it match the DL exactly is bad advice if they are the same on the DLs. The AS computers will mess it up.