Grandparents Raising Children Support Group
This community is dedicated to grandparents who are the primary caregivers of their grandchildren. In cases where the parents are not willing or able to provide adequate care for their children, grandparents may take on the role of primary caregivers. Join the support group to find support, share your experience, and get advice from other members.
It gives specific chores that are age appropriate, along with lots of other great advice.
I'm also considering this book from the British nanny: "Jo Frost's Toddler Rules: Your 5-Step Guide to Shaping Proper Behavior" by Jo Frost. Looks pretty common sense and boy, it's been a lot of years since I raised toddlers...
I searched Kindle for "grandparents raising grandchildren" and found a few.