BellaOnline Forums Family Step Parenting stepmom in need of answers

My story is qquite long and so i wont get into all of it.long story short my fiance is a phenominal father who loves his two little kids.ex wife has been preventing him from seeing his kids out of hatred towards me. We are the h.w. parents, we work with them on sports music, projects. We volunteer our time to help the kids schools and teams, we are the ones that take the children to the doctors and dentists. She does NOTHING with them but party( which is fine if you are the visitation parent).We are stuck every week making up for her lack of interest in the childrens school work and well being.Our fun time with the kids is extremely limited due to her lack of care for her kids. As per our agreement she is entitled to have the children more than us on a given month and she feels that her lying to the teachers, inability to do schoolwork with the kids, lack of good food and adequate rest has made her an awesome mom. In short i believe that since they have joint legal custody both parents should have the rights to see their children. Due to my fiance's occupation he is suppsoed to have the chidren when he returns from work and before he leaves to go to work he gives them to their mother. there have never been any issues with that ( except for the fact that she was always late and did whatever she wanted). We are cuurrently in mediation and now the ex wife has demanded that she have the kids for Christmas eve every year. Up until now we have worked on an alternating basis with rollovers in place just incase my fiance wasn't able to be in town for the holidays due to his line of work. This would be our year to have the kids for thanksgiving, xmas eve, and xmas. We will be married in 100 days and she is well aware of that. We said to her that we have no problem having fixed holidays to prevent all the confusion and unfairness involved with having the kids for all the holidays in a given year. So, we would give her Xmas eve every year ( as she demanded) if she gave us Xmas every year regardless of whether or not my fiance is working. This would eliminate rollovers and gives the children the ability to be with both famalies for the holidays and knwo exactly where they will be for what holiday. Bio mom turned around and said no way would she ever give her kids to me ( the boys LOVE me) if their dad wasn't in town. Meanwhile when she needs to go out drinking, partying, to football games, on vacation, etc she has routinely left the children with me overnight when my fiance wasnt here because she needed my help.At that point I'm an excellent soon to be step mom and she acknowledges that the boys love me. I think that's being petty and unfair. Right now she keeps calling me "the girlfriend" even though she is well aware that our wedding is coming up. Although I do get her need to want to be with the kids if their dad isn't here I could conceivably travel to go see their dad with them on the holidays. ALSO, My fiance and I are plannign to have a baby and the kids are excited, I thought with this plan in place the kids would have the ability to be with their new baby brother or sister for Xmas as well as their mom for xmas eve. This year is our first Xmas as a family and she is trying to say that if my fiance got called out to work the children cannot be with me, my family, my fiances family to celebrate but rather they have to be with her. Does that make sense? Isn't it wrong to put the children through that? Aren't we suppposed to be doign whats in the best inetrest of the kids? She also says that I have no right to pick the chidlren up from her house. The agreement as it stands now doesn't specify who picks up the kids and it definetly doesn't say that I can't. If the chidlren are allowed to go to afterschool care when their mom is working and a bus takes them to afterschool care ( not their mom), then isn't me pickign the kids up for their dad the same thing?Help!