Creating account issues

I have roughly 30 students and about 10 of them cannot make an account.  We have triple checked password requirements and cannot figure out why they are not being accepted.  Again this is effecting about a third of my students.  

I was trying to find a way for me to add the students in on my side but I can't find that either.

Please advice on how to get these remaining students added to my class.

Thank you,

Bronwyn