Right, firstly if you're trying to intervene when she's dealing with the kids, even if you disagree, you shouldn't be disagreeing in front of them as that shows parental devide and also shows her up in front of them which is going to cause a row.
If that was me and Andy was getting upset with the kids (which he has done) I would either agree with him and then later, when things calmed down, make my suggestions to him, or I would say to the kids to go and play football or do something else to give their father a minute to breathe.
Or I would go up behind him and hug him. That always works well with him at diffusing a row.
He has done similar stuff with me in the past. Like one time we got into this really horrible M talk and I could feel myself getting angry with him and I was going to argue with him and then he suddenly completely changed the subject and said 'BTW, I love your T shirt.'
Well, I was so winded at the sudden change and the compliment from nowhere that I just smiled at him and said thank you and the row was completely forgotten. You could try this distraction technique if things are getting a little heated.
And of course, remember that trivial things are exactly that - trivial. If you try to keep your mind on the bigger picture and incorporate that into your daily life then it makes money seem less important.
I got myself into debt because of having depression and I have told X recently and I just admitted it was a silly thing to do and said 'no more expensive computers for me'. Then he started talking about how he's got more money in than out, and he must be missing something.
I said yes, me, because I'm not spending all his money! He laughed at that. Making a joke out of seemingly serious things can sometimes take the seriousness away.
I guess that just remembering your love is more important than bits of paper and you won't take money with you when you die, well, that helps me.