User Account Problems Before and after Updating from Yosemite to High Sierria

[JK008]

My hardware is early-2015 Macbook preloaded with Yosemite. I have updated it to High Sierria recently. Here are the problems I'm having:

Before Update:​

1. For some unknown reason I don't really remember, login screen was problematic: I had to login through two stages: One login prompt for "user1" and after progress bar filled up, another prompt for "user2". in "Users and Groups" settings, no user other than "user2" is visible. I have never been able to use computer as "user1". I can't remember how did I set up user accounts at first.
2. I had created another user on that computer called "user3". On login prompt, you had to choose from "user2" and "user3" for login. ("user1" was gone)
   
   After Update:
3. Now, after a clean bootup, I can only login as "user3". "user2" is only accessible through logging out or switching user from "user3".

What I want is a login prompt for "user2" and "user3" on bootup. I'm fine with removing any user or changing user account settings.