Not able to join a class

I work with about 45 students this year in 2 different classes.  All but 4 were able to add me as a coach by joining our class.  All students have a school google email account.  We log in with Google & enter our email with no password.  This then takes us to our district google login screen.  We enter our school credentials which logs us into Google.  When these four click on the coaches tab to enter our classroom id there is no text box to enter the code.  It states that "For you to add another teacher, your parent first needs to check their email and create their parent account."  In the four years that I have used Khan this has never happened.  In the picture below it shows their teacher from last year which we don't have the option of removing.  We had the teacher last year, "Christy Dameron" stop coaching to see what that would do.  We logged back in and the coach was gone but we still are unable to join a class.  Any ideas?