I really need some views on this because I actually don't think I can cope without screaming.
I live in a family of four, two under fives. We are comfortably off and neither of us work full time thanks to savvy investing earlier on. We're not massively rich, just enough to live comfortably.
My SiL left her DH a few years ago and in order to fund continuing in a big house in the country said to MiL 'sell your house and I'll create a granny flat for you and you can live with me' - this was the only way SiL could afford to stay in the big house. MiL reluctantly agreed as SiL would have to move otherwise.
A few years later they moved to a slightly smaller (but stil very big) house to save money.
SiL had very infrequent specialist work which has now totally dried up and she is now unemployed with no income. MiL lives in granny flat attached to SiLs house.
SiL has announced to DH that she can no longer afford to stay in house and wishes to move but can't do so because of MiL heavily hinting that MiL being there is the reason she is not a success. 
DH has talked to me about having MiL live over the road from us in a house we rent out. We had planned to rent this house out as a source of income for the next fifteen years and then sell it.
MiL has no idea this is all happening and would be horrified to know she has to move again. She'd do it if she had to and I know she'd love to be closer to the DC (only grandkids), but she would be a hundred miles from where she's been for a decade etc.; she's also quite elderly and may need care quite soon and it would probably fall to me to provide that care.
SiL will not take just any job either. She's expecting to walk into a new career (she's not young) and earn at least £30K - preferably without having to leave her house 
I'm torn. I don't know whether to say we'll take her in (or even if she wants to come) or to say 'no you must deal with the consequences of your actions.'
Oh and there is money involved. MiL has sunk a lot of equity into the house and would need that back to buy somewhere else. Which SiL has not counted on - she thinks she can just shunt MiL our way (depriving us of the rental income), keep the money and spend it on her living costs for the next 30 odd years
.
I just don't know what to say or do. I want to support DH but I just keep want to yell 'she's a grown up, SHE needs to talk to your mother and sort this out and she should get a bloody job - any job - shelf stacking in Tesco if needs be, rather than turfing out a octogenarian who has done nothing but support her for years'. 
Sorry. It's a long post. Please feel sorry enough for me to answer or suggest anything I can do? :)