How big is your nephew’s company and how long have they been in business? Do they have financial records for the past few years and are they profitable? It seems pretty clear that this job has been created for you to get a WP which is something that IRCC will see as a warning sign that this job has likely been created as a way for you to attempt to get a WP. If this was an existing position that has become available because the previous employee left then the situation would be viewed very differently. I would suggest also looking for other job offers because your nephew’s ability to obtain an LMIA and your ability to get a WP is far from guaranteed.