The “simplest” thing most families do is to sit down and talk, holding regular family meetings (skype if far away) to get everyone on the same page. At those meetings, everyone talks candidly about their skills, interests and abilities to help each other and their parents. You will need to be very clear and organised about what they can do to help.
However, many families have great difficulty doing this simple thing. My family sought out a Certified POP Family Coach. She worked with us over time, from the beginning as we needed her until after they both died. Our coach was wonderful. She helped us learn to work together and talk — better than we had in years. She supported us in seeing that some of lived near, others far away; some of us had money, others had time, others had skills, like being a lawyer, that we could all use to make our parents’ final days as secure and peaceful as we could.
We met on Skype and she particularly helped me to keep everyone “in line” doing what they’d promised. When my Dad died (he was the second one), all us siblings and our families celebrated my parents’ great life and we’re still much closer than we ever were before the coaching.