Here's the number one lesson I learned about (and from) depression:
Don't press too hard. Talk on his terms and only go as deep as he goes. Or he may just turn away from you.

And also, sometimes, it's not about a problem or an issue that needs a solution, it's about a problem or issues that needs to be heard.

I know you are both worried about your father's (mental) health and your family's financial situation, but you have to be patient. People do recover from depression (in some cases, with the help of properly prescribed drugs due to chemical imbalance), but it takes time. Perhaps, in the financial sense, you may have to look for ways to take care of that for the time being, does your mother work? Can somebody else help out with your father's business? etc.

Whatever it is, I wish you good luck!