Please don't let them ruin or spoil this lovely time in your life OP when you should be concentrating on yourself and your own family.
As PP have said, any response from you, even Fuck Off, would be seen as a victory by them. They just want to goad you back into contact so they can hurt you some more. I know it is unspeakably awful but you know, as I do, that it is true.
You are really vulnerable right now, hence their timing. As a mother yourself, you would love, as I would, to pretend they actually care and want to be nice, to be "proper" parents that don't want to hurt/criticise/undermine you. I actually felt my mother wanted to destroy me. This is why you feel the way you do. The reality of having a narc parent is quite overwhelming.
However, you do need to establish an ignore ignore ignore strategy and stick to it. I don't know if this will help and I don't want to out myself, but here is an example of my mothers latest hoover attempt.
She is staying at my brothers holiday home in France at the moment. Although I am NC, DB had mentioned it. She went off and left her front door wide open knowing that DC have to walk right past her front door on their way to and from school. Of course DC went in, toxic nan wasn't there, huge drama unfolds. What do you think I did? That's right, nothing. Absolutely nothing, no texts, no visits to check nothing burgled, no comment whatsoever. DC contacted Toxic Nan and she said she "left it open deliberately in case they fell out with me and needed somewhere to go!!!!!!" No, mother, that's your behaviour, your life, not mine. Thanks. Totally ridiculous.
This is from years of being sucked back in and spat back out. You have to stand firm in the face of all the shit they throw at you. My DM regularly claims to have cancer. It is all bullshit.
The awful thing is that to keep yourself safe you have to remember the bad times.