Ooh this is rather infuriating, when I met DH, even though there was MIL & FIL, SIL somehow was head of the family. I knew as soon as the phone rang, it was a summons to do something tedious, or a general conversation about inane crap.
I did get it stopped briefly, as it got to a point where I'd leave the room, as she'd be on the phone most days for at least an hour, plus several more calls lasting around 5/10 minutes.
When DN arrived we put the differences aside, it resumed to how it was so quick. The daftest was planning birthdays 6 months in advance.
I'd be inclined to say to DH, we're on holiday, we've not moved here permanently. Tell MIL it's lovely for her to call, we want to relax though, surely it's more exciting to recount events when you get home.
If you can, unless there's a reason you cant, switch his phone onto silent. I don't know how much you're using them whilst away, if it's seldom, say phones in the safe (if you have one) or merely on silent till 8/9pm. You don't need constant mothering.
Just out of curiosity is your DH IRISH? There's a great TV show called Bridget & Eamon, with an episode about Eamon's Mammy, I can relate to that so much, even though we're both Irish. I only speak to family in emergency's, usually sending a text for birthdays and maybe we'll all congregate for Easter, big birthdays, children's birthdays and Christmas.