Dh and I lived in London for many years, with his parents in Poland and my parents in Norway. Not as far away as New Zealand, but illness and disabilities on both sides made it impossible for either parents to travel to see us.
We have not been able to divide ourselves in two, and have been to Poland with the kids on 3 occasions only since our youngest, now 5 was born. They adore their grandma, and she adores them. They have quality time together when we are there, she spoils them rotten, take them to the park, playgrounds, funfair, the beach, babysits so dh and I can go out in the evening?
Should we really deprive our children of this just because they are upset when we leave?
The upset and tears last a day or two, but they bring with them happy memories and experiences, of time spent with a loving grandma. Even if they dont speak Polish, and she limited English, which is a complication, but so what?
They know they have family, and family is important. Especially if you have little of it.
Now my mil cant stand me, and has behaved appallingly to me on occasion, but that is not a reason to ruin my children's relationship with her. She loves THEM, and that is important. I dont need her to love ME.
Yabu to cut contact because they adore each other and it is tough when the visit is over. Yab totally u!
Good luck. 