And if a massive climate disaster event occurs, do you think that'll be enough to convince them

For a lot of people, I do. I think many people like this are ultimately buried in their cultural context, and never had an event breaking them out of that mould / making them question what are for them basic assumptions about reality.

I think the vast majority of people are good and would care; it takes constant reinforcement to make them accept (and for many, barely, despite the image they may project) their constant participation in an absurd, evil system and to make them actively link their self-worth to it.

Also, at the end of the day, there are more and more people barely surviving and there are less and less people like your brother as time goes on; eventually we reach a critical threshold. And at that threshold there are a lot more of the former than the latter willing to fight.

You're describing the bourgeoisie. they're invested in the system because the system works for them. They don't lead the revolution, they're the counter revolutionaries.

Either (1) the system will break down so much that it's not worth it for him to support it because it no longer enables his material comfort, then he can join the revolution, or (2) as the system breaks down, he'll fight for the last remaining scraps divvied out to loyalists and become an enforcer against the changing tides. Realistically, he'll enjoy luxury and comfort the rest of his days, and his descendents will have to make those decisions.

They have a choice to make, we can't make it for them. Socialism or barbarism.

If you want a purely material class analysis of people like your brother (where their believes don't matter): for people in the imperial core, who are not landlords, but get paid high enough wages to invest significant amounts of money, but they still go to work, their class position depends first on their investment. Do they make enough money "passively" from their investment alone, ignoring wages, to live a life of average comfort if they were to quit their job on the spot? Than they are capitalists who labor "on the side", but are no longer forced to sell their capacity to work. From a revolution, they stand to gain a functioning, crisis free system, the survival of the planet, peace and the end of oppressive hierarchies. But they would lose their class privileges and have a lower living standard.

If the income from their investment is to little to live off, they are still forced to sell their labor and they are still part of the working class, no matter their lack in class consciousness. Even, if they say they are "capitalists", they are wrong. However, the working class is split and I'd like to point out two ways how: betrayal and class compromise. Examples for jobs, that try to form workers into class traitors are any jobs who discipline workers and enjoy privileges in return: like police, foreman, judges, managers with low/medium income, teachers, social workers etc. But not everyone in such a job necessarily becomes a class traitor. Some work against what's expected of them to show solidarity. This is almost non existent in cops, but very common in teachers and almost the norm in social workers even though they all have a disciplinary or controlling role, but to different extends, with different levels of political consciousness. Other privileges arise because of racism and patriarchy. Again, allies are possible who actively reject their privilege.

An example for class compromise: in the imperial core, they are likely part of the labor aristocracy and are privileged from unequal exchange, overexploitation and accumulation through dispossession. Another example: the 1968 generation dropped revolution and anti-imperialism in turn for increased personal liberties.

Keep in mind, that borders between class positions are constantly shifting with technological development and class struggle.

So what of them?

Your question cannot be answered in advance, and when it can be properly considered, it's likely you'll be the best judge of it.