IMO it does not make DT look any less negligent to point out that ST was negligent too. As far as that goes, we have no facts to say that he didn't pay child support, just that DT says he didn't, he says he did. I don't know if you have to pay child support until the divorce is final. In a legal separation while going through a divorce, I would think that the child support issue would be settled at that time, but if they had no legal separation drawn up, then the child support might start when the divorce was finalized - which was just recently.
ST being in the military, it's hard for me to believe he didn't pay child support if ordered to, because that is one thing the military REQUIRES you to do. Plus, DT living near a naval base, she and all the kids were entitled to have a military ID card. Her's would be voided when the divorce was final, but the kids could still have one as long as ST was in the military or retired on disability until they became 18 or (24, if attending college). The kids' ID card would have entitled them to health care at the naval base or any other military health facility, so that is part of their support. Now, I do not know if they had this or not, because I do not know the circumstances of ST getting out of the military. I don't know if he just voluntarily got out or was medically discharged. If he was medically discharged, depending on the percentage of disability, I think he would still be able to keep his military ID card and have one for his kids - if say, it was a 100% disability.
As for ST not being able to visit the kids before Somer died, we don't know the reason for that either. I remember hearing that he did not have the funds to go to the funeral and donations were made for that purpose and a van provided. I don't think people would have made these donations for him to visit the kids if one of them had not been killed.
It just seems like these poor kids were not too well cared for by anyone. Of course, that is only my opinion from what I have heard and read. I have no way of knowing if reports are true.