If they have competed for Ukraine, Ukraine would have to release them to be able to compete for any other country.... They may be forced to wait for many years, and there is no guarantee that they will eventually be released.
Katerina and Ivan have now got official documents that they are not members of the Ukrainian Federation. It's not a release but can it be used instead of it? It actually means that Ukraine doesn't want them on the team. Or should they get the release as well?