From what you say, I suspect your nephew has misunderstood what God wants him to do with his life — maybe not in the future, but certainly right now. Perhaps some day the position he hopes for will open up — but in the meantime, he has a responsibility to do what he can to take care of his family.
The Bible teaches that we have a responsibility to take care of those who depend on us (such as our families). This seems to have been a problem in one of the churches Paul had established; for some reason, a few people refused to work and were depending on others to take care of them. His reply was blunt: “We gave you this rule: ‘If a man will not work, he shall not eat’…. Such people we command and urge in the Lord Jesus Christ to settle down and earn the bread they eat” (2 Thessalonians 3:10,12).
Please note that this wasn’t spoken to people who couldn’t find jobs (as is unfortunately the case with many today). This was instead directed at people who had every opportunity to work — but refused to do so. The Bible repeatedly warns us against laziness, and urges us instead to be diligent in our work: “Whatever your hand finds to do, do it with all your might” (Ecclesiastes 9:10).
I realize your nephew may have other problems (such as depression, which can paralyze us). But pray for him, and as you have opportunity confront him with his need to be more responsible.