DS is still a boobie junkie at almost 17mo. I haven't considered weaning him because it is most definitely a primary source of sustenance for him. He eats solids really well, but I would estimate about 40% of his nutrition still comes from Mom.
That being said, if I am not around, he doesn't get milk. He's old enough that I don't pump, but I also don't leave him for more than 8 hours (and thats only been one time). He eats other foods, drinks water or smoothie, etc. and my husband doesn't have a problem comforting him or my now 3yo DD.
I would be concerned if Nana has 14 kids at once, and is pushing you to wean because she can't soothe your little one. She is most likely tired, but Nana doesn't have time to tend to her nap schedule if her hands are that full. Yes if you were there you could calm her more easily, but it shouldn't be too difficult to distract her for that last hour until you can give her special mommy loving.
Best of luck, I can't imagine that having your CCP giving you grief makes things easy. You are doing the right thing. Hopefully she will work with you to make things easier for herself and your DD.