Your brother is wrong and unrealistic, and YANBU, he is.
Of course.
However...I graduated in a recession (over 30 years ago), rather shell-shocked by an awful final year, and with no plans except a desire to earn my own living and keep a roof over my head independently of my parents, and so I took crap jobs with no clear strategy on how long I would be doing the crap jobs or how I was going to go about finding a career path that would lead to something other than more crap jobs. And I'm afraid that, although it was starting to come right by the time I was about 28/29, that slow start did hobble my confidence for a very long time, well into my 30s. Still affects me now, to be honest, but less so.
So...I would say to your brother, take the crap jobs, because money, good qualities on your CV, self-respect, fairness to your family - but don't stop thinking and working towards what you really want to do, and make sure you keep on that path, while you're stacking shelves and cleaning.
I suspect some of the 'rather be homeless' bluster is just that, bluster, and he's actually terrified of leaving university in the middle of a global shitstorm. He'll be alright, but he has to keep working and planning. Lucky for him he can come home!