Effective usage of parallelism requires some basic knowledge on how parallel machines work and how parallelism is implemented in QUANTUM ESPRESSO. If you have no experience and no clear ideas (or not idea at all), consider reading Sec.3.
Please see above.
A frequent reason for lousy parallel performances is a conflict between MPI parallelization (implemented in QUANTUM ESPRESSO) and the autoparallelizing feature of MKL libraries. Set the environment variable OPEN_MP_THREADS to 1. See Sec.3 for more info.
If the same data work in serial execution, use
code -inp input_file instead of code <
Most likely there is a misspelled variable in namelist xxxx. If there isn't any (have you looked carefully? really?? REALLY???), beware control characters like DOS control-M: they can confuse the namelist-reading code. If this happens to the first namelist to be read (usually "&CONTROL") in parallel execution, see above.