xanax will help/abate the PHYSICAL withdrawal symptoms - shakes, fast heart rate, agitation, hallucinations etc. The dose will need to be adjusted based on how much he drank.
However, xanax (or any kind of benzodiazipine) is also a depressant and when taken with alcohol (also a depressant) can be big bad trouble (pass out and stop breathing) if you are not careful.
Good luck to both of you and please take care of yourself!!!