I know that many of the posters here do not share this view, but I think that grandparents are immensely important in the lives of children, even if some problems come with it. Especially now that mom does not want to speak to you. They are still family. This does require balance and patience, but I do not think you have anything to fear from occasional visits to grandma's house. Your children will not like it if grandma downs you to them and will likely report back anything negative she says, so you can change the arrangements at a later time if it becomes necessary.
I do not want to be like the cold selfish organization that uses children as pawns. These are their relatives, and they should grow up deciding for themselves the course they wish to take in life. Undoubtedly they will side with your views as you are their mom and do not take them to any Kingdom Hall. In fact, you could take them on a Friday evening and pick them up Saturday evening to eliminate any threat of them taking taking the kids to a Sunday meeting.
I just hope family love prevails and your children are not deprived of those who care about them. I think grandma will soften over time and look for occasions where "family business" needs to be discussed.
Remember, at one time we felt as your mom does. It is not her fault. She is torn and trying to please God as she wholeheartedly believes is right.
