Sharing fillable PDF forms via email

Hello, I have two separate questions, albeit related.  

I need to send fillable pdf forms (created in acrobat DC) to users who have varying pdf reader/writer programs on their computers.  The files need to be password protected.  (These are report cards that previously would have been shared only on the server at the school.)  Our teachers do not have remote access to this server.  They need to be able to input their information and then pass that exact form (with password protection) along to another teacher for additional data/editing and eventually to administration for final editing.  I would prefer that they not have to "save as."  Is there a simple way to set up the file so that it will save as a fillable form and can be passed along?  Or is it dependent upon the program they are using which unfortuately varies...  At this time we don't really want to do a shared online file.  Thank you!  

The second question is simliar.  I have a 4 page fillable form with student information that I would like to email to families this year and have them correct any errors or input new information for the next school year.    When sending en masse, do the forms have to be flattened...which would defeat the purpose?  Is there a recommended way to instruct the families to complete and save the file (provded I can get it to them)?  They already have a lot of trouble just submitting the form (when I distribute the original).

My thanks for any advice you can offer!