Have you tried willfully misunderstanding them? When they want you to do something or are hinting with the delicacy of a brick to the head. Behave as though they're doing you a favour you need to regretfully decline.
We need to come and live with you for an indeterminate length of time, and be complete PITAs!
Oh, no, PIL we couldn't expect you to do that! It's so kind of you to think of us, but no, really, it would be far too disruptive for you! Why, we'll be working and blah blah, it wouldn't be fair to you at all! No, really, we couldn't put you out like that!
You need to give SIL money. And a kidney.
Oh, we couldn't possibly! So sweet of you to suggest it but poor SIL, I'd hate her to think we think she needs charity! No, no, I know you're only thinking of us but really, it's far too much to put onto SIL, I wouldn't want her to feel obligated to us in any way. I know how independent she is, it would only upset her. No, really, we just can't, it's not fair to her at all!
Other DILs do more for their PIL!
Oh, I know, and I'm so grateful you're not like that! Gosh, that would be awful wouldn't it, if I was interfering in what you were doing all the time!? Can you imagine! It's so good you're so independent - especially at your age, too! Marvellous really! Must be such a relief to you that you're not dependant on anyone else? That would be terrible, wouldn't it.