How would you help?

My daughter called me today and told me that there is so much drama going on with her future inlaws she just doesn't know what to do. Her husband to be has parents that got a divorce about a 3 years ago and his dad has been dating a woman ever since. This woman is not well liked by the children and she is upset that no one has invited her to a bridal shower. First the woman or the father did not come to either my daughter or his son but instead to one of his daughters. That got everyone upset. Then on father's day his kids decided to cook for him at the lake and went out and bought everything and he brought her and her son he took her son out onto the boat right away and spent no time with his kids not even to come in and sit down to eat. The kids are 22, 18 and 17 so not small children. Well they all ended up back at my daughter's house she had spent the day with her father. When she suggested they talk to their dad and tell them how they feel they were like oh no we have never talked about our feelings with our dad we can't do that. My daughter has a hard time understanding that since even though her father and I were divorced when she was young we all still were very open and communicated very well together. We always respected each others feelings it was just how we were. So now there is a shower coming up not to mention the wedding next month and the kids are mad at their dad and with his girl friend. I told my daughter that it would be bad for everyone if that relationship didn't get put back together. I told her that she needs to explain to all of them that family is important and even if they don't like the woman that she is with their dad and that she should be invited to the shower since it is his side giving it and she should be invited to the wedding. I also told her that she is going to have to sit down with her future husband and tell him how to communicate with his father. I reminded her that she is good at communicating and as his soon to be wife she needed to make sure he could do it as well. Of course he and her communicate very well and have a wonderful relationship so hopefully she can walk him through talking with his dad. I really had to bite my tongue though because for heavens sake the dad seems to be acting like the child and that drives me nuts. How would you help? I just don't want any drama to spoil this wedding.