don't waste your time, you are just going to make a messy situation - worse. If your attorney is urging you to file for sole custody, be concerned, as he/she is more looking at your wallet than your interests - or the kids.Sole Custody?Hi, this is a very difficult situation and I'm sorry to hear about it. I am assuming at this point in time that you have joint custody but that you have physcial custody (your kids live with you).
Unfortunately just because he is missing mediation doesn't mean that you have justification for sole custody. The courts would perceive this as your problem with him. It is very difficult to get sole custody these days.
Think about his interactions with the kids:
Does he skip weekends that he has visitation with the kids? Does he ever call them at the house? Does he feed them when they are with him? Does he keep them well clothed (in the winter are they dressed appropriately - you don't have to provide clothing for his house)? Do the kids regularly take showers or baths at his house? Do the kids enjoy their time with him - or does he get the kids and then get a babysitter and go out?
Even if your answer is negative with every one of these items, doesn't mean a change will occur.
Being the devil's advocate - think carefully about your reasons for changing to sole custody - you have physcial custody and control over much of what the kids do - is it just so you don't have to deal with him?
The courts often assign a child advocate lawyer for the children in cases like this. It's these folks' job to determine what's going on: whether (1) the kids are safe, and (2) if the parents just have a problem with each other. These folks are known to give the parents a lecture and send them off to counseling with no change occurring in custody (even in cases where the kids were sexually abused in the physcial custody parents' house - as long as the perpetrator is out of the house, the kids are deemed safe and will remain with that parent).
I don't know if this helps you or not. It's a really difficult situation and no simple solution. Be the bigger parent - make all your appts (and on time) - document all his missed appointments and any issues that you might have. At some point, the courts will take all this into consideration but you have to have all your ducks in a row.
Good luck!