Through an agency (Home Instead) we got a live-in carer, primarily for my father. The agency insisted they only do two weeks at a time so it was disruptive. The range was enormous - there was one who went AWOL in the night and had clearly gone clubbing and lied about it. It was enormouslky expensive (2k a week - the price having gone up by about 20% within six months).
Then my father's needs were such that he needed an additional carer in the morning and evening but they had to come for a minimum of an hour. Then the live-in carer's breaks needed to be extended as he'd wake in the night so it got to the point that we had two live-in carers, especially since my mother was leaning into having everything done for her.
Obv this was EXHORBITANT - in addition to all the costs of the house. It was also very disruptive and there was constant beef between the carers and the agency that we'd get sucked into. And we were lucky in that my parents were extremely courteous and polite, with a very nice house in the centre of one of UK's nicest cities, so it was quite the hot ticket for the carers.
My father died about six months after the hiring of the second one. We dropped down to one live-in carer - I don't think my mother would have needed this if we'd been starting from scratch but she'd become accustomed. In fact, she was furious about us getting rid of the second one. She really took to the life of a dowager duchess with servants. She has dementia.
One carer was way better than the others - able to organise things like fixing the washing machine, getting the GP, getting the dog to the vet etc. She was saying she was leaving the country and we just knew we couldn't manage at a distance with one of the other carers (who'd ring up to say things like the Sky dish wasn't working without even turning it off and on). OMG the constant issues with the online supermarket account.
Sorry this is very long and I'm not sure of my point. Other people I know have found carers who they pay directly (much cheaper) and have done it for years and it's been fine. We found it untenable for much longer than as an emergency measure in my father's dying months. The goalposts are always shifting and from our, possibly selfish, point of view, it has been much more straightforward now my mother is in care home in our city. We visit much more as our time isn't taken up with all the other admin.
To be blunt, I think it depends on how long you think your MIL has left. Less than a year, yes muddle through with live-in carers. More than that, a move to a care home would be better.