Have you tried following your thread back after it shreds and breaks to see where it is getting hung up? Maybe if you go very, very slowly, you will be able to see where the problem is. If you haven't tried sewing with a sandwich of different fabric, I would try that. Is it possible that there is a hidden piece of lint or thread in the bobbin case or the tension disks? So sorry about your DH. Best of everything as you work through your loss.