Invest what you can afford to survive and not all the money at once. You can divide the income into two and use one part for the investment and the other part to do things in the family to avoid quarreling. Invest wise.
I hope that he wont do that because I have read some newbies that did invest and did the wrong decision of investing what they cant afford to lose. And when they are in need of money, they were forced to sell the bitcoins that they have bought. While the situation of the market was unfavorable, instead of making a profit, they have made a lost that they have regret. That is why you are right that he shouldn't invest all that he has got.