TheBakeryQueen, not all families are big enough or strong enough to pull together though.
I have seen lots of different sides to it.
MIL looked after her own DM at home for 20 years, all while DH and his siblings were growing up, and GMIL was bedbound for over a decade of that time. She still has her DBro living in an annex to their house, he turns 70 next week and has been a double leg amputee (due to childhood polio) since his mid-20s. So she is his carer as well (he is somewhat independent, but couldn't manage without the CONSIDERABLE support MIL gives him). But MIL was a SAHM and her own MIL was the district nurse so able to get a reasonable amount of support and knowledge through her, and the support of the community around her (that's the kind of community she lives in - they do all rally round and help).
Both my grandmothers died in the past year. And 1 grandad 3 years ago, the other 19 years ago. So I knew them all well, and saw the reality of looking after them all.
My Dad's parents looked after each other for more than 20 years. DGM was weak (heart issues) and had other health issues, but still lived at home and had a reasonably full and fulfilled life until around the time DGDad died. One of their 6 DCs that lived still lives at home (eldest girl), and although FT working until 23 months ago, was home every night. 3 other DCs live within 10 minutes drive, and all those spend a lot of time there - 1 DD came a lot of afternoons after school (teacher), while another DD and her DH did the gardening and spent time in the evenings, a DS used to bake them buns and also spend time there. Another DS is abroad now but was local enough for many years and both those DSs would often call into "home" for their lunch and be company in the middle of the day. The final DS lives 3 hours drive away, but would be up for work reasons nearby pretty regularly and spend time those evenings or lunches that he could. DGD went into hospital 10 weeks before he died, as he had a mini-stroke and then a series of them meant he deteriorated and died. But the family all spent a lot of time there at the time (I only really got to see him by calling at afternoon visiting by taking late lunches from work myself, as there were too many there at nights).
DGM was starting to get weaker at that stage and lose her short term memory. 1 of her DDs retired 5 months after DGD died (took early retirement, which she planned but had thought her Dad would be around as they planned to work on editing his book together). Live at home DD still worked, but arranged working from home in mornings initially (only went to office in afternoons most days). And they were lucky to afford private help so carer came in first a couple of afternoons then increased amounts of time. That DD retired almost 2 years ago now, so both retired girls did much of the physical care, with paid help, teacher DD did some too but has health issues of her own, while the local DS continued the social visiting for company and making the buns so she would eat. Both further distant DSs came as much as possible and again were company for all the girls (DGM and their DSis's). They were lucky enough to afford a stairlift, paid carers, bought physical aids and knew how to arrange other help such as renting commode, hospital bed, wheelchair etc. But all 3 were skin and bone by the end of it. (DGM was comfortable and happy in her own place, but it was a big combined effort of the family). I work FT and have DD with SNs as well as DH spending 50% of his time overseas for work, so couldn't call whenever DD or I had a cold or anything (effect could be disastrous on DGM) and I rarely could leave DD with anyone else (not a lot of family support here, except all those involved in caring for DGM). So I would write, phone, and call when I could, bringing baking or homecooked meals for DAunt to heat for herself at least. And I spent more of my little spare time caring for my other DGM on the other side of the city. They were aged 91 and 93 respectively when they died.
My Mum's DF had a stroke when I was 9. DGM rehabiliated him home from hospital, got him walking and talking again, and looked after him well. Over the following decade, he had a series of strokes and she rehabilitated him every time and he was home for most of that period. She got 1 hour of home care a week, although I think towards the end she got a 2nd hour. 1 DD was living 3 hours away, another was overseas, and her DS was trying to rear his own family too. They helped as they could, but DGM did almost all of the care. DGD had another stroke just before my final exams for school, and spent about 5 weeks in hospital before he died, aged 76.
I spent a year living with DGM some while later, before DH and I got married. She was still ferociously independent - I was allowed stay as there was a clear plan for me leaving (wedding date set) but she wouldn't have anyone stay permenantly. As the "boy" stopped cutting grass locally around that time (late-20's lad!!), DH took over doing it for her every 3-4 weeks and we maintained her garden from then on (we were actually cutting the grass the afternoon before she died). When she was aged 94.5, she was the "super sub" on her local bowls team, which won the Division 2 league! But she started to lose her short term memory, and also started to fail physically. I had been filling her freezer with dinners for 1 for more than a decade (I'd make a couple of small shepherd's pies or fish pies when I was making them for ourselves, and bring them when we came to do the grass). 1 DD was now in the city and also brought dinners, and brought DGM to do the shopping regularly (also worked outside home and had a DH and 2 DSDs to raise herself). Other DD would fill the freezer when she was up and do cleaning etc, and sort paperwork, appointments etc. DGM had managed, due to her own age, to keep the 1 hr home help weekly which kept the house basically clean as she started to fail, and the homecare team was able to increase to more personal care visits as time went on, up to eventually 3 times a day. But she needed FT care as she was a danger to herself (almost blew the house up a couple of times, burnt out pots numerous times, had a number of falls etc). She went into hospital a couple of times for long stays, starting really just after Christmas last year and only getting home for a couple of weeks after that - she moved from the acute to the long stay part of the hospital (lovely bright rooms looking out onto parkland, with deer coming into the gardens to feed at dusk and plenty of plants which she loved) 10 days before she died. Again, I had done a lot of visiting to hospital - but there simply was no option for caring for her at home at that stage. And she was happy there - she loved the banter in the dining room, they had a lovely party for her 95th birthday, she was well cared for in clean, warm, comfortable surroundings. And she had plenty of her own things (small rug we'd bought her a few years back, her own paintings - she took up painting in her early 70s!, her own vase for flowers, and others) so it wasn't alien. And she was able to get around as it was flat, they had plenty of walkers and then wheelchairs as she needed more help, and people who were able to help her when family weren't visiting. And as a staunchly independent woman, there was no way she'd accept help at home from her DDs or me in any event. Open visiting meant all her buddies were able to come when they were able themselves, and I was able to come a lot of days from work at lunch as well (which was easier than going to her house - not only in terms of distance and actually having time to drive there and back, but being able to arrive and then leave without the palaver of locks and feeling upset leaving her alone and needing more help but having to get back to work.
All you can do is do your best to look after the person in need of care and make sure they are getting the physical care they need and still getting plenty of social (care is the wrong word, but I don't know the right one - not just visiting but , yes, caring) from you as you are able. Knowing that they are not abandoned but still loved and cared for and part of your family.
DH and I have talked about it ourselves, for our own parents. We live 3 hours away from them all, and cannot physically care for them. My own DM has said that we should put her into a nice home and not feel guilty, she just wants a hairdresser to visit regularly (and not have a comb over), and for us to "bring a tweezers to keep her chin hairs plucked". I know I cannot contemplate having any of them in our house - it's not suitable and we are not there enough (we both work FT and, as I said, DH is overseas a lot), quite apart from being right out of their own circle of friends and supports. But we will support getting them the right care for their needs and maintaining a lot of caring visits ourselves. And hoping that all the various family members will do this as well (smaller family for DH and half of mine are overseas), but knowing that it will probably fall to us to take the lead in decision making, funding and visiting on both sides.