Thanks everyone, I really do appreciate your comments and advice.
Some progress today...perhaps...
I took the kids by myself for a whole day out (for the first time so a 180 and GAL) to somewhere really great that W had often mentioned but we'd never been to before. W didn't know where we were going and I know she had been trying to find out from the kids. They couldn't tell her because they didn't know either. I just said it would be a fun surprise. It would have been the first time ever that W wouldn't have known where the kids were - so a 180 for her.
The kids had a really fantastic time. W came to collect them, and she looked amazed at where we had been. I was really happy and content having had a good day. I didn't invite W into the house (she would have said no anyway) I just left the door open. W said she was going to wait in the car but then came back and walked into the house. I was amazed because a month or so ago she'd had her legal person send a letter saying she'd never go into the house. I kept away busy in another room. I didn't offer her a drink. W saw me doing some washing-up (which had been her one chore) so that was another 180 for me. I'm very independent whereas W has her parents doing everything for her.
W stayed for an hour. From what little I noticed she looked awkward. Upon leaving with the kids W said "I love you... tell Daddy you love him, go on tell Daddy you love him". W never normally says such a thing, but she'd might ask them to thank me. I won't read anything into it because a few weeks ago she blew me a kiss when leaving with the kids. I think it's just for the sake of the kids.
I don't trust anything at all W says or does. I know from experience that she appears to be nice just as she is about to do the next hurtful action.