Step kids and ex-wife are horible to my partner

hi, I hope there is someone out there that may be able to have a solution to my predicament, My partner is currently going through a divorce with his ex-wife, and whilst his is happening his three grown up children now 19 20 and 22 yrs of age will not have anything to do with him, they have all totally dis- regaurded him, and i strongly believe that his ex-wife has everything to do with it, about 18months ago his eldest daughter and i were getting on ok we were talking and for some unknown reason she just turned on me and started to give me all the filthy looks she could find and started to ignore her father. This has been going on for just over a year now, and it looks like that she has taken her mothers side, and so have the other two. What gets me is that none of them will approach their father and ask him why he left in the first place! they all refuse to see it from his point of view, yet i have said to his eldest daughter that she could come and visit when ever she wanted , but she never has and now , i fear that she may regret it later on in life as, My parrnesr eldest daughter now has a child of whom will be two in september and he doesn't know his granddad at all as she will not come anywhere near him or bring his grandson to see him and get to know him. I feel that this has something to do with his ex-wife and that she has told my partners three kids that many lies that they do not know what to believe. In the end i got to the point where i just smile at his daughter but don't speak as i've taken the view that i and my partner have to get on with our lives , but it means getting on with our lives without his kids , in which i would rather they would be a part of their fathers life . what can i do it is heart breaking for my partner as he has no place what so ever in his grandsons life. It's as if none of them want to know their father.