Unfortunately, DH keeps caving into pressure from SW.
She has capacity and has said she wants to go home.
So here we are. Trapped
I feel for you OP, and your DH. You're just on the cusp of not quite far enough away for SS to have to step in, no matter what, and yet just close enough to 'come running'.
My DPs lived too far awary from me and my siblings when we got to this stage. That had been their choice, they knew they wouldn't have any family support around them in their later years.
When the inevitable happened, Adult Social Care had no choice but to step in. Both DPs were incredibly stubborn about staying at home (my DM was in hospital for over 70 days following a cardiac arrest, my dad was very infirm, and yet they insisted my DM came home when the hospital discharged her, and despite my objections, was told 'they have capacity'.
Trouble is, my DPs hadn't told anyone at the hospital that none of us lived anywhere near them (think in terms of a different country) and it was only when I managed to tell Adult Social Care in their area what the reality was that anything happened.
But, OP, once I did that they really did swing into action and I can't fault them on that. Once they know there really is no family support they can, and do, provide services, and/or will point the way to private providers if your DP's funds will support that.
Every case is different, but you and your DH really have to stop running every time the phone rings, otherwise they will think you can cope. And you know you can't. It's shit, I know it it, but you have to say 'no, we can't do this' before they will listen to you. And your MIL has to accept you can't do it either 