@Happierwithouthim, he's struggling to keep a lid on things, isn't he? Not showing himself in a very good light either mediation or with the solicitor 
Arrangements with the kids need to be way more structured. THEY need to know what they are doing and when. Shift work is one thing, but choosing overtime at the last minute over the kids? WTF? I'll be surprised if they are even bothered about seeing him when they are older if this is his attitude. Hope you can pin something down properly, for everyone's sanity 
@RoseMartha, I hope you can get things sorted access wise too. Yes, a 'relaxed approach' benefits no one apart from him, whatever spin he tries to put on it.
I've just found more credit card receipts. So as well as screwing me over directly financially, he's also running up debts. Perhaps i should speak to my solicitor about this.