Thank you everybody for your kind supportive posts and please forgive me for not replying individually.
The weekend was ok, better than expected. DH is - touch wood - coping with the chemotherapy very well so far and is entirely himself. I wasn't sure what to expect but, for the moment, everything is just the same. It is almost easy to block out the reality of the diagnosis and, in a way, that's the best thing to do - to just live for the day. We are together and as happy as we always are. If anything, the diagnosis has made us even closer and DH gave me a lovely card for Mother's Day, saying he loved me more than ever (which made me very weepy, but also grateful).
DDs 2 & 3 arranged for some flowers to be delivered and DD3, who opted to stay in London so not to put us at risk, face-timed on Saturday and Sunday. Apparently, one of her close friends has just come down with the virus, so she is sure that she made the right decision in not visiting, but misses us all a lot. She was so worried about DH but also about DD2 and me, as we are both asthmatic, so in the 'at risk' category. However, she plans to come in 14 days (if London has not been locked down by then).
I am proposing to try to keep busy, at is the best thing to do, and keep looking at the grass out of the window and saying 'I will cut you tomorrow' 
. DD2 has a list of films for us to watch so the enforced isolation has its upside, that we spend time together and just do simple things. I also have the latest Hilary Mantel (courtesy of DD2), which should keep me out of mischief for a while, and we were lucky enough to have an Ocado order on Friday, so we have plenty to eat.
DD1 called on Saturday and we spoke for a while. she seemed different somehow, or perhaps it is wishful thinking. About half way through the call she wanted to swap to FaceTime, so she could see me, and did look quite 'loving', asked how I was feeling because she knows how much I love DH and said she was 'there' for me. She had DGD2 with her, who is very sweet.
DD1 said that they hadn't sent any Mother's Day cards and hoped that was ok. I said fine, it's how you treat people all year that counts (any irony was lost but I didn't say it in any barbed or malicious way, just trying to be positive). I said it was her Mother's Day too, but she said that she wasn't expecting anything and that she thought it was a day for reflection. In fact, she used the word 'reflection' twice, so perhaps she genuinely is reflective - who knows? I was a bit reluctant to pick up the phone, to be honest, but it was better that I did.
She said how pleased she was that we had visited and is convinced that DGD1 remembers us, especially DH. She sent a video in which she said that DGD1 was talking about him, which may be true, but may well be not. However, clearly that is what she wants to believe. I said we might visit in July depending how everything was, but she was quite non-committal. I doubt we will anyway, for lots of reasons, and probably it is better to keep things as they are, at least for now.
I am pleased that we made the visit, as is DH, and it is fortunate that we went when we did, as it was probably the last opportunity, but I am not terribly keen for a repeat just yet, even without all the other stuff going on with DH's health and the virus etc. Upon reflection, LB's parents were nice and I am sure that they meant well - which is all that matters, really - but I think perhaps his mother was a bit insensitive in keep telling me how DD1 was like her daughter, given that she knew that I had hardly seen or heard from her for several years. I think, if I were in their shoes, I would have maybe handled it a bit differently, as I have inevitably been dwelling on it and thinking that she is DD's mother now and the DGDs' grandmother. But there is no point in such negative thoughts. We went, it was fine, now we are back and have other things to focus on. By striking some sort of amicable contact, it lessens the emotional burden, which I don't have the energy for right now.
Ghost, so sorry to hear about your DH's friend, keeping everything crossed for him.