I agree. Unless he was really lazy and stupid, or just plain cocky, no killer would dump bodies so close to where they lived and risk the bodies being discovered. Plus, from what else I've read, people/kids walked through the pathway near where they were found, to go to the store, and someone who lived in that trailer park would know that, too. That's why I think it was a dump job, someone who knew the area but didn't live
nearby. I also think it was done in winter or else the bodies would be buried, but that's my conclusion, it has no basis in fact.
If you have the time, you should watch the raw press coverage video released last November. It's fascinating and has a lot of information in it. But, to answer your question, they have limited DNA profiles on each of them, but they did compare the DNA of all four of them. The results were: the woman, the oldest child and the youngest child are maternally related, but the second child is not known to be related at this time. That doesn't mean they aren't, just that the DNA associations that they have available don't match so they don't know. They explain it better in the video. Here's a link to it- it is long but worth the watch, IMHO: