The VO will not mention your brother's condition as a refusal reason. Given that your brother does not have any strong ties + he is dependent on your dad, it would indicate that your brother would overstay his visit.
Unfortunately, your dad does not have any strong employment ties as his business is seasonal. That's another negative that you'll need to work on.
As tough as it might be, you will need to take a few steps back and look at your parents' and brother's situation unemotionally..... detached from the desire to have all three of them visit you at the same time.
Unfortunately, it will not be possible for all three of them to visit together..... it won't happen from a visa perspective (at least not for your brother). It won't be an easy decision for you, but you'll need to be practical.
I have suggested the strategy for applying for your parents' visas. Do think about it
Unfortunately, your dad does not have any strong employment ties as his business is seasonal. That's another negative that you'll need to work on.
As tough as it might be, you will need to take a few steps back and look at your parents' and brother's situation unemotionally..... detached from the desire to have all three of them visit you at the same time.
Unfortunately, it will not be possible for all three of them to visit together..... it won't happen from a visa perspective (at least not for your brother). It won't be an easy decision for you, but you'll need to be practical.
I have suggested the strategy for applying for your parents' visas. Do think about it