Ugh!
My sympathies w/you OP on all of this!
The reason this child is acting like a holy terror is because both his parents as well as his three sets of Grandparents are letting him rule the roost which is something that any 10 month old should never be allowed to do.
If they do not nip his behavior in the bud right now - the consequences will be murder later on down the line.
You can discuss your issues w/his parents & fill them in on what you are dealing with.
Perhaps kindly suggest that they in turn try to get their own parents not to be so lax in their treatment of this child.
Hopefully you can all work together in finding ways to help this child understand that he is not the one in charge…..that the grown-ups are + that while he may not like to do certain things > he has to do them and that is that.
Because that is the ONLY way this issue will ever resolve.
If they are unwilling to take the steps necessary to change this boy’s behavior, then it is entirely up to you if you can continue this position w/the current dynamic.
Good luck in whatever you do!