I feel like I'm going to get angry at my little brother while he's sick.
Why would you get angry at your brother while he's sick?
He was behaving as if nothing was wrong with him and we had to spend a lot of money on his treatments.
It seems your brother was trying to be strong even though he wasn't feeling well. You should be more understanding and supportive of your family by not causing trouble with your brother.
Yeah, but that would be too much out of me and my family will appreciate it if I got tough with them.
I strongly suggest you try and see things from his point of view. I'm sure he's still very grateful for the treatment.