I'm sorry that he's had to go through so much.
Other than Jevtana, the only approved drug I don't see is Xofigo for bone mets. There are third-line hormonal treatments - estrogen patches and ketoconazole.
I can only come up with one clinical trial that he might be eligible for. It's at MD Anderson in Houston:Study of Selinexor (KPT-330) in Metastatic Castrate Resistant Prostate Adenocarcinoma
I compiled a list of medicines that could he could potentially get off-label. You can forward it to his oncologist to see if he think any are worth trying. Some of them are inexpensive, fairly safe and readily available (e.g., statins, metformin, hydroxychloroquine, depakote, Celebrex). Others are expensive. No one knows what their true efficacy for prostate cancer is, although, because they've been approved for other purposes, their safety profiles, good and bad, are known.Drug Repurposing for Advanced PC - Introduction