My understanding is the first one is the primary one, and will be used most of the time. The second one is the fallback and will be used if the primary isn’t reachable
Usually you’d have two different addresses from the same service to configure DNS
Listing addresses from two different services would get you a slightly inconsistent experience, where every once in awhile a different block list will be used
I saw the need help signing in option. But after entering name and phone number, I had to enter last 4 of SSN, which I think is harder to find out
Additionally, afterwards I got an email that my user ID was requested