I have two boys 13 months apart, so I do have an appreciation of what it is like. As far as the daytime nap goes, both my boys grew out of their nap at about that age, and the only way to get them to sleep was to go for a drive or a long walk. We used to drive until the fell asleep then find a good place to stop and have a nap ourselves - not sure if that is an option for the grandparents - other than that , going for a long walk and totally ignoring them also used to work.
I think that their night time routine is out of sorts because they are overtired, if you can sort that out, the nights might become easier. I take it she does all the usual bath time, calm atmosphere, dimmed lights, warm milk and quiet story stuff already?
Another trick that worked for us was to have them sit on our knee and we pretended to be asleep but holding on to them, if you breath deeply an rythmically, it seems to calm them and they soon drop off. Only danger is that you sometimes drop off as well!
The fact that everyone else is so stressed will not be helping, so they need to try to be as chilled as possible as the boys will pick up on the stress, but that is easy to say and difficult to do in the circumstances.