Sending big hugs and lots of sympathy Misty. Our adult children can be so cruel can't they? Sadly, it seems as though your daughter is modelling her father's behaviour.
In my case, I believe SIL was instrumental in turning my daughter against her family. We are sort of reconciled now - or at least she thinks we are - but she ghosted us for six months, moved without telling us her new address, got married without telling us for 18 months and, worst of all, didn't tell us about the birth of DGD1 until she was 14 months old.
Now, her father, my beloved DH of 33 years, has been diagnosed with terminal cancer. The 'reconciliation' had happened previously, and DD does seem very concerned about DH, but I wonder if she feels any remorse at all. DD is wholly selfish, I am afraid, although SIL has made her more so. She is still not speaking to her sisters - I think she would like to, but they don't want to know - and has dropped all of her friends. Part of me thinks that she is in a controlling relationship, but she has been complicit in what I can only describe as the abuse of her family.
Anyway, I am not writing this to make it about me, just to say that I think you need to try to come to terms with the fact that this is not a very nice couple. Don't expect a fairytale ending - even though my DD is in touch virtually daily, the hurt and anger still go very deep, especially as I feel most anger on my DH's behalf, although he has already forgiven and moved on. His diagnosis puts things in perspective, as does this virus nightmare.
My advice is to try to be realistic and recognise that, sadly, by chasing DD and SIL, you are playing into their hands and giving them power. I don't know how old they are, but they may improve with maturity and your grandchildren are likely to want to develop a relationship with you when they are older, I have no doubt of that. This has recently happened to a friend of mine - no contact with his DD for years, but DGD is insistent on forming a relationship. My friend has also suffered from an aggressive cancer, which his DD knew about, but didn't visit him. How do you move beyond that?
You deserve better, you just need to lower your expectations of DD - at least that is my experience, if you don't expect much, you won't be disappointed. As others have said, concentrate on yourself, when things are back to normal, go on some lovely holidays etc, make new friends. Don't be dependent for your happiness on people who don't care. Build a happy fulfilling life and you will be a lively, buoyant, fun, resilient person when your DGC come to find you.
With regard to inheritance, I have three DC, so am leaving each one a one third share, to be divided with any of their children, so at least SIL and DD will only have just over 10%. But, in your shoes, I would try to spend as much as possible on myself anyway. They don't deserve it and, if there are any more remarks about inheritance, I would just tell them that you will leave them a token legacy but the rest is going to the local dogs/cats home, favourite charity, gnome in the garden etc.