First of all, they of course are not going to get any money. But when they think they are going to get the money, you can see how Ivan thinks its going to change their marriage.
It appears that their marriage is okay at the start of the story. But as Ivan daydreams about what will happen after they've won, you can see how their marriage would fall apart if they got the money. Ivan is already feeling angry that his wife's relatives will want some of the money. And he is feeling that his wife isn't good enough for a rich man like he thinks he'll be.
So in general, what's going on is that the money is going to cause a huge change in their marriage. Sudden changes are hard to deal with. And it looks like this change is going to make Ivan, at least, dissatisfied with his wife and jealous of anything that will take some of the money out of his control.