I'm with everyone else who said that it is definately not normal that these dogs mess in their crates.
Years ago, we had a dog in behavioral classes, and the trainer said that a dog would not mess where it sleeps. If a dog does, the crate is either too big, or the dog has behavioral issues. Well, that dog did. He messed his crate over and over again, and would not stop, and his crate was very small. Unbeknownst to us, he had come from a puppy mill(she told us she was a "breeder". We were really naive then), and had serious mental issues from inbreeding. Anyway, my point is, with him, it was behavioral and extremely abnormal.
We have a chi mix right now, and aside from the issues *she* has from the way she was raised, she does NOT mess her crate. She has a really small crate, and one of the few things the people we got her from did right, was that they crate trained her.
So, I don't think that this messing their crate thing is a chi issue, or even a food issue, since you're stopping at 6. I think your dogs need a behavioral eval very soon.
We have always been told by our vets to never feed after 8, and only twice a day. Our dogs get their food in the morning, and then again around our dinner time between 6:30 and 7.
I agree that you should limit how much they eat, and definately have them on a very strict diet of only one food. No table scraps, no mixing foods. Get a good premium food, and only feed a small amount each time. Pick it up as soon as they're done eating, but definately leave their water.
Working on the amount and when you feed, changing to a very small crate, and addressing the behavioral issue hopefully should help these dogs.
Best of luck to you that it gets better. I know it has to be very hard on you taking care of an infant and having to go through these challenges with not just one, but two dogs.