how i can convert Simultaneously three docx files to three tei files?
You can do the conversion on the command line using for example docxtotei; so you could write a script to invoke that command three times successively. It won't be simultaneous though -- conversion is an inherently linear task!
Alternatively, you'd need to modify the underlying XSLT itself to open your three input files simultaneously. Don't forget by the way that a docx file is actually an archive containing several files.