AIBU? Mil and expecting care

[Bidendoesnthaveaclue]

Could do with some advice.

We moved closer to MIL a few years ago, along with DHs sister.
DHs sister moved away and left us with MIL.
DHs other sister is upset thinking she now has to uproot her life and move here to care for MIL... MIL has told her not to worry as myself and DH will care/help her.
I'm psychically disabled and a few years off a wheelchair I won't get better and my disability shortens my life span. We also have a disabled DC. So as you can imagine we have a lot on our plates. I can barely dress or wash myself!
I'm upset as now on top of everything we're expected to care for MIL as she gets older , it restricts us a lot from going on holiday/going away visiting family as one of us will have to be here to help MIL at all times.
AIBU to feel put out by this? She's well aware of our struggles but still expects us to care for her.

I can't understand why old people nowadays haven't run through a few scenarios in their minds including - what happens when I can't get about.
The previous post war generation didn't expect to live into their 90s, their parents hadn't. Care homes ads, insurance for funerals, savings advice is everywhere nowadays. I don't get how they can sit back and assume X will take care of everything. Inexcusable.

Personally I’d text them all and explain you were a bit surprised to hear you and DH were expected to be mils carers. Explain you don’t have physical capacity to be mil carer and ask them to discuss how they plan to share the load as it can’t fall on DHs shoulders as he won’t cope