control vs. letting go, what is ok to tell?

So, in separating from my estranged spouse with untreated ADHD (we are living in the same house but hashing out a separation agreement with an agreement for one of us to be moving by 1/1): 

How much do I just let go, and let him do things or say things that may affect my children badly, and when should I intervene or explain to others my perception of the circumstances? What is the line between badmouthing my ex and explaining the truth? 

For example, I usually pick our children up. My spouse has difficulties remembering details and being on time, and our kids' school and activities are generally managed by those who are fairly straightforward about this: parents need to be on time to pick up their kids. So I usually do almost all of it just to avoid any issues. Yesterday, my spouse (who got up at 2 a.m. to work on his car and woke the whole house) was supposed to pick up our child after school. He realized that he had left something on at 2 a.m. and when he went to start his car to pick up our child the next day, the battery was dead. Long story short, he went to a neighbor who drove him to pick up our child. In the meantime, he was 25 minutes late, our child and the teacher with him did not know where he was, and my child was worried. My child said, "I was the only one there. My teacher did not know what was going on." (The entire time, I was close by and had my cell but he did not call me. It genuinely does not occur to him that this is a big deal for everyone but him. And if I try to talk to him about it, no matter how I do it, I promise, with all of my heart that if I tried to just explain that our child was worried and that he needs to make sure he will be on time, even if it means starting and checking the car an hour beforehand, he has to make this happen--it will be world war 3, he will insist that he DIDN'T KNOW and it was NOT HIS FAULT, which seems to be his only concern, and that I am blowing everything out of proportion, and we will get nowhere. And it will, indeed, happen again someday soon). 

OK, a bit of a rant: this happens every, every, every single time. There is ALWAYS SOMETHING that keeps him (poor victim, he tries so hard and it is NOT HIS FAULT) from being on time. I told him that morning that it was important to be there right at 3. On the dot. Early, even. And I know, sure, folks can have a dead battery, but it is the millionth time that something occurs that is "out of his control" that keeps him from picking up our child on time or being on time for a teacher conference or kid's doctor appointment. And he decided to work on his car at 2 a.m., woke us all up by accidentally setting off the car alarm and banging in and out of the house several times, and forgot and left something in the car turned on. If it were the first or second time, I would not even think about it. But there is just ALWAYS some kind of situation and drama and mostly I am worried about my children. I get ADHD and I do not fault that he has trouble with this--I fault that he is so pathologically defensive about it, and so concerned with not being blamed and not being "criticized," that it is impossible to address solutions with him. Ironically, I had a dad who was often late or fell asleep when he was supposed to be there and pick me up, and I grew up worried about it. In the end, I have accepted the fact that he will not be a different person, but I am worried about the effect this will have on our kids growing up and what to tell them about it. 

Here are my questions. Go ahead, give it to me straight: 

-We are separating and ultimately divorcing. There will be times he has to pick them up, because he will have partial custody. How much do I tell my children's teachers, my children, etc. about his "issues" and have a back up plan in case he is late? Can I tell them that he has issues being on time or do I help my children have their own backup plan and just let him screw up? (They are young and don't have their own phones or anything). What do I tell them to explain why their dad is late when none of the other parents are? 

-Their teachers and counselors are wondering what is going on. Why can't our family pick our children up on time? Should I tell them that my spouse has issues and to call me if anything happens? 

-Should I just fix it so that I am the only one who picks them up? I know this is crazy, but I have had a decade of drama with this person and I just can't take much more. I want to have to deal with him as little as possible. 

Thanks, everyone--my therapist told me that I can't control what he does or says, and I know this. Unfortunately, he is wont to say bad things about me to them, and I know I can't make him be on time. I just need some ideas for dealing with it.