these coins are worthless?
If what the others have been saying is true, then yes I believe this would be the case. If on the 1/1/18, they took a snapshot of XIOS and forked it into the new coin, then only those people holding XIOS in their accounts at that date will be eligible for the new coins.
At least, that's how I think it will work. I am not sure why Yobit would sell coins after this date? But if they are, it would explain why the price has tanked because people are selling the coin as it is no longer being maintained/pursued by the developers and you can still get the new coin as its after the cutoff date.
It was on 1/5/18. They moved the date. The team also mentioned something about Yobit having issues with the withdrawal of Xios, which caused a lot of people missing the fork. They are working on resolving that issue. Go on their discord to talk to them.