Absolutely praying for your dad, you and your brother.
Hesitant to mention this because I don’t know the situation, but that sounds similar to some of the early signs my dad exhibited with what we eventually learned is dementia. His showed up in his early-to-mid sixties. There was a sudden drop in activity and an inability to recover from it. He dealt with depression at times, but it became a whole different animal once dementia emerged. He retreated from everyone. Covered his windows and didn’t want to be around folks aside from his kids and grandkids. A neurologist could help to assess. And the basic assessments they do are really low key. Praying for you.