Just wanted to mention that in this scenario through my testing with R1 the username is ignored.
"Verify settings for VTY lines on R1; both username and password are actually the line password, because there are no local users configured:"
Based on your comments it seems you are hinting they must be the same.
R1#telnet 150.1.1.1
Trying 150.1.1.1 ... Open
User Access Verification
Username: aldfkj
Password:
R1#
R1#
Also is there a reason why you used a non default method list on R3? I got it working with the default and saved myself two commands :).