I've been financially assisting my brother, who lives out of state. Due to caregiving costs, I no longer can. Any advice?

What else can you do except be forthright? In the process of telling him of your new situation, being unable to afford to help him financially, let him know that you will investigate what other help might be available to him. And then do your best to do just that.

First off, does mom have resources that are being tapped for her caregiving? VA, Medicaid should be accessed before your resources are used. Second, is it Mom or you who is providing support for brother? What are HIS options. I would, preferably in person, have a serious conversation with him about "the family's" financial situation.