In our league (20 teams - 2 conferences) there is always someone who can't remember a password or worse their username at season start. I can see the email address for each franchise carried over from the prior year, so I just tell them to go input the email on the league site and indicate forgot password like you do for pretty much any website today. I also send a franchise invite email from the commissioner/franchise setup menu. I then check back with them to make sure they got in. I think you can also see this in one of the franchise activity reports.
It isn't perfect. I actually like team owners having to be responsible for their own access. In the past, when commissioner had more access control, I had one owner who was non-committal except when he wanted to be. Of course this would always be about 5 minutes before the Sunday 1:00 PM kick off when I'd get a call that he can't get into the site and could I get him access or input a lineup for him? Meanwhile, I'm trying to manage last minute changes to my own team.
I do like having as much control as possible as commissioner, but I guess I don't mind not being able to manage passwords. MFL "help" section usually has the answers to questions, but it takes sometimes it takes some hunting to find it.
Okay, all that said, I hope we actually have a season this year. Getting the site ready and going to be sending out invites in July.