Another Church cannot step in out of their own initiative. If one Church feels the need of someone else coming in and giving them a hand, they would reach out to a sister Church and ask them to intervene. You will see this in Acts at the First Council of Jerusalem. You will see the result of meddling by those who claim to be from the Jerusalem Church who turned out not to be officially from them. And you will see that the Jerusalem Church didn’t step in until Antioch sent Paul and Barnabas to Jerusalem, and this is only after they tried to resolve the issue by themselves and couldn’t come to a conclusion.
You will see this during the Soviet era, when Ukrainians came to North America they didn’t want to be under the Russian Orthodox Church because there were questions on the influence of the Soviets on the heirarchy back in Russia. So the UOC in Canada and the US are, until today, under the EP as they requested the EP to take them. The EP did not step in and took them out of her own initiative, it is by the request of the Ukrainian Church, at least those in North America.