Estranged adult child
Welcome to the forum!
It's a shame your adult daughter no longer wants to be in contact with your husband. If you have defended your husband (which is understandable), then she may have extended some of the negative feelings towards you. Is your daughter's male partner as up in arms about the disagreement as she is? It's good that you have tried to mend this family rift. However, your daughter will probably need to sort this out directly with your husband, as the disagreement involved him. If your husband and your daughter's partner are able to come to an understanding about the disagreeable situation, this would help to pave the way for this family distance and tension to be resolved.
Try taking a step back from this situation. So, try not to email or ring your daughter too often. If she feels pressured, she might feel the need to stay distanced or even retreat further. It sounds as though your daughter might need time to get over what happened, however minor it may have seemed to others. Some people, simply because of their personality, find it hard to let go of issues and are stubborn, which makes forgiveness more challenging.
It's good at least that your daughter does still contact you sometimes via email or phone. It's a real shame that you and your husband cannot see your granddaughters. Hopefully, with time, your daughter will realise that the presence of her parents and of her children's grandparents in her life is important. If you don't mind me asking, how long has it been since the disagreement?
I hope this situation can mend itself over time.
Family disagreements are so upsetting, but very common and to stop you having contact with your grandaughters is unfair as they are the ones who will pay the price for their mothers resentment at this time and as you live some distance from them it makes it harder, I assume you daughters partner is also somewhat controlling the decision to ban contact because of the disagreement which is unfair, he is not the biological father is he, if so he has no right to make that kind of decision, if he has a problem, then its between the adults and has nothing to do with the children, but yet is using them as pawns in a game, very immature behaviour.
Keep the contact up when the girls are at their dad's house, so they know they are important to you, it is not teaching the kids good resolution skills, your daughter should never put someone above her own children, she can only control them until they are 18, they will then make their own decisions, I'm not sure how old the girls are now.
Partners will come and go, but your children are forever and their needs should over ride anyone else, I can understand where you are coming from I have two little grandaughters and I would be so upset to, maybe there is some miscommunication between her dad and partner, but without resolving it the problem will create more of a rift, keep trying to talk but don't be door mat, people treat you how you let them, so keep your boundaries and she will hopefully come around.
In the mean time carry on with your life and I'm sure this will eventually settle, just be there for the girls and show them a loving caring grand mother.
All the best