"Grandma and Grandpa decided to give to others who are truly in need this year for Christmas - isn't that great! The gifts she typically would get each of the grandkids didn't cost a whole lot on their own but the amount together can make a real difference for someone in need."
I grew up with a Grandma who had 14 kids and 35+ grandkids. There was no way she was getting gifts to anyone kid or Grandkids for Christmas.
The other grandma would get something minimal ~$20 for each grandkid. She made sure she got everyone the same gift. But it took a lot of work and a lot of money to make it work.
If she had decided to do something like your parents are doing I think I would have understood.