This is stated in an article by Iryna Romaliiska for Censor.NET titled The War for Citizenship in the Sea of Azov - The Story of the fish trawler Nord.
The article says that two crew members did manage to fraudulently leave the country by air.
"After two unsuccessful attempts to leave the mainland Ukraine, the Russians found a way out - they issued Russian travel passports to Crimean fishermen. These were the IDs that two crew members - Dmitry Tarazanov and Irina Oborina - used to depart from Kyiv Airport on April 19. They started spinning stories about being in the ‘Ukrainian captivity’ as soon as they arrived on the peninsula," the article reads.
The State Border Guard Service gives the following formal explanation: "Two Ukrainian nationals - members of Nord crew - fraudulently left Ukraine for Belarus. Two alleged citizens of the Russian Federation checked in for the flight to Belarus at Kyiv Airport. While undergoing the passport control, they showed IDs of Russian citizens issued by the Consulate General of the Russian Federation in Kharkiv. But since the spelling of their names in Russian passports differed from the one in Ukrainian IDs that were entered into the database, these persons managed to cross the border and left for Belarus."
When the border guards realized what had happened, they checked the next flights and found out that seven more Nord crewmen were going to try to leave the country in the same manner.
There is no confirmed information about the current whereabouts of the remaining crew members while their lawyers, who were previously very willing to talk to the press, have been dodging phone calls for several weeks now.
Sources in law enforcement agencies familiar with the matter told Censor.NET that after an unsuccessful attempt to escape through the Kyiv Airport they are hiding on the territory of the Russian embassy in Kyiv. Ukrainian law enforcement officials suggest that the Russian diplomats will try to smuggle the fishermen out.
"Firstly, they can make an attempt to cross the border illegally - beyond border crossing points or through the sections of the border beyond government control. Secondly, there are plenty of blank passports in the Russian embassy so they can receive IDs in another persons’ names, cross the border, and then make statements that they allegedly crossed the border with their own passports ... There are a lot of options," a source in a law enforcement agency familiar with the matter told Censor.NET.
A source who asked not to reveal his true identity says that this situation can be resolved via political means as well. For example, Ukraine would allow crew members to leave for the peninsula with showing no IDs at all and later make formal pronouncement that "we understand that these are Ukrainian nationals who are forced to live in the occupied territory where they have families. So we allowed them to leave mainland Ukraine as a matter of humanitarian and moral compulsion..."