Thank you all for your responses, I'm so glad I posted here . I am on mumsnet but am looking for those in the same position as MiL and not myself, and I am grateful to have your perspectives.
I have also asked my own Mum what she would like me to do if she was in the same position and she just advised to give MiL time to find her place in the changed family dynamic and make her feel welcome whilst she is doing so.
Thank you for all of the suggestions, I like the idea of DD making something for her that we can attach a special note to. DH speaks to his Dad regularly but I was also thinking that perhaps I could also ring her once a week (outside of our visit) to let her know how the DCs are etc. DD does sometimes have one to one visits with PiL when DH and I have things to do that are no fun for little ones but I can make this more often which might make her feel a little more needed/useful.
FiL also (unintentionally) might make MiL feel more insecure as if he visits without her will comment to her (when MiL makes observations on the DCs) that DD 'always does that' or that DS 'doesn't like to be held that way' which can't make her feel all that good about it either. I might see if DH can intervene on those occasions perhaps to reassure MiL.
I think that the observations of not having daughters of her own are spot on too.
I know that it also needs MiL to relax and realise her important role in our DCs lives but I'd love to assist with this and not allow anything to sour our relationship.
Being moved along by someone who "wants your place".
sticky labels on apples - remove before washing!