Last Christmas, I gave my 6 and 4 yo kids tablets. I sometimes sit with them while they play kids'games. The 7 yo plays on a couple of sites that allow her to dress characters. Just last week, I played a word game with the 5 yo. She is learning spelling and matching the number of letters to the number of spaces. We go to the library for books because they prefer reading a book they hold in their hands. They also like to go to the library to play educational games on the kids' tablets. These games are different than those they get on their own tablets. For the last few months both use adult tablets. Their parents check up on their use from time to time. Once in awhile this makes it easy to talk about use and why some is not helpful.
The 7 yo is on the Autism Spectrum. Would be called Aspergers before. She uses games to stay calm and watched kids' programs. So does her older brother who also has Aspergers. He started research when he was about 10. He likes to tell us what he's learned. He has difficulty having conversations.
So I'm not sure why you object to tablets. Of course they are too young for phones. I download kids books on my kindle. The girls prefer real books. Their parents and I are avid readers. The 6 yo reads books. The 5 year old seriously wants to read. Sometimes, I help her read words in games.
I wonder how your husband talks with his parents. Does he just tell what not to buy? And what to buy? My daughter and I have conversations about their goals as parents. All year long we have conversations off and on about things they'd like for theire kids and what I'd like to buy. Together we make a Christmas list. I definitely have more money than they do. My daughter and husband express gratitude for what I'm able to do.
I suggest that the abundance of gifts and your dislike might have more to do with your and their son's relationship with them than with the actual toys. I suggest that you lovingly talk with them about how grateful you are for the gifts as a start of a relationship in which you work together on a gift list. Instead of telling them what you want them to give, share your family values. Talk about what your kids are involved and interested in. Talk about the special needs of the 8 yo and what sort of things that will help her. Recognize that the grandparents may be buying what they would've liked at that age. I noticed at the beginning I did that.
I know if my daughter was critical if my choices and that I over indulged at Christmas time, we would be estranged. I would feel criticized and unloved.
A few years ago, my daughter suggested I bank money for education past high school. I've opened an Oregon cCollege savings account for the oldest. That money is tax free. I've named the younger kids as beneficiaries on investments. I'm very pleased to know I will be helping with education after I'm gone. It did take me a year before I was able to do that. I love gifting. Gifting is my love language.
I suggest if you focus on love and gratitude, you will be able to work those negative, critical feelings out even if the grandparents continue to give more than you'd like.
I grew up poor. Being able to gift is important to me. My children are also poor. They are glad to receive my help.