Advice? Personal situation

So I'm a young ftm and my daughters father hasn't been in the picture since I found out. At 29 weeks he completely changed his mind and wants to be in her life. I'm now 22 weeks and he has yet to tell his parents. His excuse is he's "in a good spot with his parents right now and doesn't want to ruin it" well he's 19 and still living with them, a high school dropout. But the worst part is, his mother is sick (I'm not sure how sick, I just know she's not healthy) and in worried she could pass before she knows she's getting a granddaughter. How long should I give him? He says he'll tell soon but that was 2 weeks ago! Should I just tell them myself? It's eating me alive