I don't know of a way to change the attachment names when sending an email in Forms. An easy way to do what you're looking for would be to send the form and attachments (or shortcuts to them) to a single folder and, via Workflow, email the contents of that folder. Put a search activity that looks for the folder right before the email activity, and on the email activity configure "The selected entry is a:" to "Folder". Then select "Properties" next to "Folder" and choose "Attach a copy of the folder's contents, expand the "Show Document Properties" link and select "Attach copies of the documents", along with any other options you want to use.