I have not seen TH calves at this stage of gestation so I certainly am not an expert of any kind here. The only sure way to know is to send these calves in for necropsy as DL has recommended. I would also urge you to contact Dr. Beever and send him whatever samples he would like to see.
I have learned a long time ago to never jump to any conclusions on these type of events. From the pictures, TH seems to be a possibility, but then I have seen some aborted calves that look very strange that were caused by other things. To me the only thing I see that strongly suggest TH, from the pictures are the abdominal hernias. The back legs do appear to be abnormal but to my very amateur eyes, they do not look as abnormal as the TH calves I have seen. If you have seen calves with TH you never forget what they look like. I would urge you to follow the proper chanells and find out what you arr dealing with. Mother Nature also has a few tricks up her sleeve, that can really confuse us from time to time.
Dumped twins at 4 to 6 months happens at a fairly high frequency. It certainly would be nice to know if this is caused by something genetic in nature, or something else.