Chamonix,
Your DP needs to get it into his head that in the UK grandparents do not have automatic rights of access to their grandchildren. IIRC I have mentioned that before. Your mother's logic here is not appropriate either. His parents are not people that can at all be reasoned with. It is NOT your fault or his they are like this; their own birth families did that lot of damage to them.
If they are too toxic for you to deal with they are certainly too toxic for your child. They have done a great deal of emotional harm to you both; you simply and absolutely cannot let them see your child.
A percentage of the general population is dysfunctional and/or abusive. That percentage, like everyone else, has children. Then those children grow and have children of their own. The not-so-loving grandparents expect to have a relationship with their grandchildren. The only problem is, they’re not good grandparents.
Many adult children of toxic parents feel torn between their parents’ (and society’s) expectation that grandparents will have access to their grandkids, and their own unfortunate firsthand knowledge that their parents are emotionally/physically/sexually abusive, or just plain too difficult to have any kind of healthy relationship with.
The children’s parents may allow the grandparents to begin a relationship with their children, hoping that things will be different this time, that their parents have really changed, and that their children will be emotionally and physically safer than they themselves were.
Unfortunately, this is rarely the case, because most abusive people have mental disorders of one kind or another, and many of these disorders are lifelong and not highly treatable. (Others are lifelong and treatable; however, many people never seek the necessary help.)
The well-intentioned parent ends up feeling mortified for having done more harm than good by hoping things would somehow be different — instead of having a child who simply never knew their grandparents and who was never mistreated, they have an abused child who is now also being torn apart by the grief involved in having to sever a lifelong relationship with the unhealthy people they are very attached to.
If you do both want peace from these people you all need to go no contact with them. I am not altogether convinced even now that your fiancé could cut them out of his life.
They were not good parents to the man you are planning to marry; they are not good grandparent figures to your child and will do similar harm to her as they have done to your fiancé. Protect your most precious of resources from these people. You will come to truly rue the day you allowed them any access whatsoever and you will kick yourself roundly.
Such people like his parents will take a mile; they will ignore any boundary you care to set and the emotional harm to her will be done right in front of your very eyes. They have already overstepped here by messaging you back rather than their son. They will continue to do so, they will take your actions and use those against you as well.
This excerpt re narcissistic grandparents could help you as well:-
"You are the parent. You get to make these decisions without apology or excessive justification. You can assure your child that you are making a wise and loving decision for them as well as yourself. I am not going to script what you should say because you are the only one who knows your children, but you must convey that this isn't up for negotiation. This is not a decision that the child gets to make. Yes, children usually love their grandparents. Children are often quite indiscriminate in their love which is why they need parents to guide them. Not every person is safe to have around and this is a good time to teach that important life lesson. The more matter-of-fact you are, the more matter-of-fact your children will be. When we act hysterical, they will usually reflect our hysteria. If you act anxious, they will act anxious. If you appear unsure, they will push. Model the reaction and attitude you want your children to adopt.
If you have another set of grandparents in the picture then focus on them. It is rare that both sets of grandparents are nasty. Emphasize to your children how much we enjoy being around grandma and grandpa so-and-so (the decent and loving grandparents). Cultivate your children's relationship with the decent, loving grandparents. Teach your children to be grateful for the decent, loving grandparents. Gratitude is a highly effective antidote to loss. Focus them on what they have, not what they don't have. Model that attitude of gratitude.
You will find that the children will eventually stop mentioning the loss of the grandparent if you are not bringing it up. If you are talking about your grandparent in the hearing of your children then you are inviting them to keep talking about it, too. I can not over-emphasize the need for your explanation to a younger child to be calm, pragmatic, measured and short. Long explanations make you look defensive which will tend to peak the interest of the child and prompt him to push the issue. You can gauge what is appropriate information depending on the age of the child. If the child is older and has experienced or witnessed the grandparent's nastiness in action then you can say more".
You can and should now renege on this arrangement made with them (I sure as well that they did message you back immediately; they were waiting for that).
Many adult children of toxic parents feel torn between their parents’ (and society’s) expectation that grandparents will have access to their grandkids, and their own unfortunate first hand knowledge that their parents are emotionally/physically/sexually abusive, or just plain too difficult to have any kind of healthy relationship with.
The children’s parents may allow the grandparents to begin a relationship with their children, hoping that things will be different this time, that their parents have really changed, and that their children will be emotionally and physically safer than they themselves were.
Unfortunately, this is rarely the case, because most abusive people have mental disorders of one kind or another, and many of these disorders are lifelong and not highly treatable. (Others are lifelong and treatable; however, many people never seek the necessary help.)
The well-intentioned parent ends up feeling mortified for having done more harm than good by hoping things would somehow be different — instead of having a child who simply never knew their grandparents and who was never mistreated, they have an abused child who is now also being torn apart by the grief involved in having to sever a lifelong relationship with the unhealthy people they are very attached to.
Your DD will NOT blame either of you for protecting her from her malign and toxic grandparents. Blood is not binding, you are protecting her from bad things.