Missed Visits, Becoming Frustrated- NEED ADVICE!

I could really use some advice dealing with our current situation - if there are any seasoned FPs or people who have suggestions on how to proceed I would GREATLY appreciate it! We have been fostering a now 4 year old boy and his now 3 year old sister since Labor Day weekend. They had been removed from their home two weeks prior and were in a temporary home until a match was found. For the purposes of this long tale, we'll call them Bean and Butterfly. I'm too tired to think of anything less cheesy and more creative! They were severely neglected when they arrived, with the little boy almost non-verbal and communicating with grunts, and the little girl covered in open, infected sores and lice. They hadn't been to a doctor for a wellness visit in two years, were underweight with poor muscle coordination, etc. I could go on and on but I know many people here have had experience with children who have been neglected - it's not pretty. Suffice to say that it's been a long road, but they've made incredible progress and are thriving. Their bio Mom has been involved in visitation from the beginning, but bio Dad has just started in the past six weeks or so. Mom has always have 2X a week visits, so Dad was granted the same. There was a PFA in place for quite some time, so the state agency feels that joint visits would be inappropriate. Mom lost custody of an older child to grandparents twice in the past and then again this past summer. She knows the drill, and always presents as very cooperative and agreeable. The issue is that both parents have consistently cancelled roughly 50% of their visits. The excuses are always different - car broke down, sick, car impounded, aunt died, called into work on an emergency even though they were newly hired and hadn't completed orientation, depressed, doctor's appointment, etc. The cancellations are also always same day, an usually last minute. Just last week, to give you a for instance, Dad cancelled both of his visits and Mom cancelled one of hers. Dad cancelled again yesterday and Mom cancelled today - after promising the kids they'd see another older sibling and go roller skating. This is typical - Mom makes grand promises and doesn't deliver. Pizza. Presents. The park. Then, she cancels, shows up late, leaves early, or "forgets" to bring what she's promised. Mom cancelled two visits the week of Christmas and didn't give the kids presents until after the New Year. The presents were mostly used things they must have had at home, and we had to keep some of the stuffed animals in the shed because they reeked of smoke and we were afraid of fleas. She also cancelled a birthday celebration just a few weeks ago. She was a no-show for IEP consultations that delayed speech therapy for her son by six weeks. You get the picture. For months, I have called and spoke with both the state worker and the parent aide from the third party that monitors the parents and their visitation. I've explained the impact that the lack of consistency has on the kids and the devastating affect that disappointment and lack of trust has. I've asked that if they're going to continue with 2X a week visits even though Mom and Dad each usually only made one, that the parents not promise things to the kids they can't deliver. I have been assured numerous times that the parent aides and social workers will speak to them to ensure they're not building up the kids for things they can't deliver. As today's cancelled skating rink visit shows, that clearly hasn't happened. I'm frustrated, and have been for months. I love the kids and have bonded with them and I feel like I need to be their advocate. In my opinion, the state puts the desires of the parents over the well-being of the kids. When I asked about cutting down on scheduled visits I was told that wouldn't "look good for the parents." The GAL told me that it's something she will mention at the next court hearing - six weeks from now. I feel like my pleas are falling on deaf ears, but after the kids had been with us for a few months and we saw the parents playing the game and doing the minimums to stay in their programs, getting kicked out of drug counseling, and skipping visits with no consequences, we made a pact to each other that we'd be a voice for the needs of the kids. To break it down, they are supposed to have M-R visits, two with Mom and two with Dad. Each visit requires them to leave school early and be dropped off here at the house after the visit is complete. Once a month sibling visits are later, and in theory they're visits that will include dinner. My biggest concern is the lack of consistency that the kids are experiencing, along with the obvious pain broken promises are causing. We worked so hard to get them on a schedule since they were not in nursery school or daycare and didn't have specific times to sleep and eat. Now, six months later, they (and we) don't know what the day will be like 4X a week. The four year old is learning days of the week and understands that certain things happen on certain days. He is very sweet, sensitive, and empathetic. He has had his heart broken over and over again. Our entire lives revolve around this schedule. Because I teach, the amount of time I can stay after school is determined by when they're supposed to be home. There have been days when I left a meeting early only to come home and find out the visit was cancelled. This means I had to turn around, travel 25 minutes in the other direction, and pick up the kids. There have also been times when I was stuck and my husband had to take a half day from work in order to pick the kids up and get them home. We can't plan anything four afternoons/evenings a week because of visits that may or may not happen, and it's starting to get really old. Still, I'm an adult. I can deal. I can reschedule and scramble and make it work. The kids can't. Am I being unreasonable? Am I being selfish? Am I so clouded by the love I feel for the kids that I'm making a mountain out of a molehill? I just feel like this has been allowed to go on for too long and neither parent is being help accountable. They're both supposed to show up for a doctor's appointment tomorrow. If they do it will be a first, but that's the kind of luck I have. Coming off a streak of 5 out of 8 cancelled visits, including tonight's promised skating party, I feel so angry that I don't know how I can be in the same room as they are. Any advice? What can I do? What should I do? What voice do I have, if any, to advocate for some consistency for the kids and our family?