Sorry to hear you're caught up in one of those "whatever you say/do makes it worse" situations. In the past I have sometimes, though not always, found that a "Sorry if I've upset you (meaning both DS and DiL), I didn't mean to" often helps.
Unfortunately, the last time I did this, the response was "Stick your sorry where the sun doesn't shine" All I can, and am doing is waiting it out until DiL relents
HildaW has a lot of good advice there! I would add that including something along the lines of - What CAN I do to help?; - since I am/was ill I just don't have the energy I used to - etc etc.
I am tempted to ramble about my own situation but everyone's is different. Not EVERYTHING is ever your fault, you are doing the best you can
What were the first ever records that you bought and when?
Parents-in-Law. What do/did you call them?