My wife was the youngest child of a second marriage. We were in our 20's when we had her parents to take care of. We moved a trailer to the family property a year and a half into our marriage and over the next ten years, took care of them. They died 20 months apart. Their biggest fear was "being put away" in a nursing home. My wife did promise them it wouldn't happen. We were true to our word.
My wife was able to quit work just before our only child was born. Before the child was 2, My MIL was diagnosed with cancer. The next year was a major trial on our health and well being in general. I was working nights, so I would come home, stay up into the afternoon watching our daughter until I could get a little sleep, just to go to work again and do the same thing the next day. As primary caretaker, it was like my wife was working full time again. The emotional toll was tremendous, especially since my father-in-law didn't like the idea that the attention wasn't all on him, and he certainly acted out like a toddler would. His philosophy was that if you treat someone badly and they stay, they must love you. After my MIL died, he, grieving and still needing to feel in control, would call other family members lying that he hadn't see us in days and we just left him alone. They would call and jump on us and not believe what we told them. In all that time, we never left him alone. He stayed in his own house, but we had an intercom between the houses, and we both spent quite a bit of time with him every day.
My wife's brothers barely came to see them at all. One couldn't stand to see them, and the other said "just call me when he's dead". My FIL's controlling nature took a toll on the whole family. 16 years later, my wife still has the scars from his mental cruelty, but feels that she stood her ground to the end and fulfilled her promise to them. We both agree we did our best by them, and would do it again. We did in our 20's what most do in their 50's. We could have used the experience in life of a 50 year old, but didn't have it to draw on.
All in all, I think there will be trying times, but the main variable in the mix is this: What is the attitude of the parents? Are they realistic about what is happening? Pride is one thing, but beating your children over the head with your pride is something else. How much help you can be is only as much as they can bring themselves to accept. Make sure you and your spouse have earnest discussions and agreement on what's best. Believe me, the DH of the caretaker daughter is commited as much as she is. Every so often get a sitter and take some time for yourselves. THIS IS CRUCIAL!
My parents are 74 and 69, and as of now are still completely independent. There are 5 boys in the family, and no girls. We have all had discussions about who our parents would move in with. Competitions are more like it. We are all pretty much are ready for it. My wife is like the daughter they never had, and they are like the parents she never had. She is ready when needed to do it all over again, but this time with parents who actually appreciate it. There is a very realistic view from all sides about the implications. This will be so much different than before. Thank God for that.