You can't get blood from a stone. Make sure they have it.
Talk to the wife. She may care more.
That don't work. Forget about it. Just don't shoot again for them.
The wife doesn't care more. She's the one that initially responded, with a very cold, annoyed-sounding email with the payment schedule, which was immediately followed-up by the husband, who apologized for her "seemingly cold tone", and then reassured us they would have the payments made by the projected time-frame.
Forgetting about it is also not an option. -- Dude is living off photography full-time and every penny counts for him right now. He doesn't have a day job to fall back on, and while his workload is increasing... it was just/is wintertime. Winter is slow. Which means money is slow.
If they're needing to spread out payments, that's something I can work with, but they are seeming to choose to lie about the situation, rather than being frank (this is, of course assuming, it doesn't come tomorrow.)
*I'm* not the one that even set the payment schedule or the amounts. That's what she came up with. If the situation were worse, I would think the response would have been a "We can't pay this right now", or more payments broken up into smaller amounts.