I am on two of Happykid’s accounts, and she’s on another one with me that is left over from when we were out of state for two years and she was in charge of dealing with our house for us. My mother was the second person on the home-town bank account that was opened when Happykid was born, and after she passed away, my sister who is local to that bank became the one on that account. Happydad’s mother is on one of his accounts so he can send her money easily. Happykid is on two of my credit cards and one of Happydad’s. So yes the financial connections can look messy to an outsider, but all of these people are responsible and we are set up to take care of each other when someone needs a bit of help.
I think that difficulties are more likely to arise if there are multiple children in need of fairness, or if one (or more) of the parties involved is a bad money manager. We’ve got only one kid, we are down to just one grandma at this point, and everyone is (for the present at least) financially responsible. What works for us won’t work for everyone.