To be sister churches they had to be distinct. Can you describe this distinction before the fall of Constantinople, and before the Unia of Florence in XV century?
Were there are another "sister churches" like that? How this differentiation was affected by the 1299 move of metropolitan see from Kiev to Vladimir (closer to Moscow) after the destruction of Kiev by the Mongols?
My turn to not understand what is written. Bolsheviks defined borders of Ukraine? If that's what you meant then I'm in shock. Here's an insight- Ukrainians existed before Bolsheviks.
The Ukrainian republic was created by the Soviet government. The eastern border was drawn by the Soviet government and this process of expansion was done with Khrushchev adding Crimea. As a result large lands in the east which are ethnically and historically Russian became part of Ukraine. Western border of the Ukraine was drawn by Soviets when they took Lvov area from Poland and easternmost part of Czechoslovakia. Northern was drawn when Soviets decided where the Belorus is. Southern border was defined by the creation of Moldavian republic.
These are some serious question which would require more research on my part (I hope you're asking because you're interested in this matter, and not just pulling my leg.) For now I'd just say that it happened, that metropolitan of Kyiv was established, then some centuries later it was subjected to Russia.
Other "sister churches" are just branches of Orthodoxy- Armenia, Syria, Serbia, Ethiopia etc. For example Georgia, which if I recall, along with Armenia had one of the earliest Orthodox churches and simply had to be on par Moscow's. And yet Georgian Church became part of the Moscow Patriarchate.
The Ukrainian republic was created by the Soviet government. The eastern border was drawn by the Soviet government
That's 1922. But in 1918, 4 years prior, a little event took place- Ukraine had declared independence. The Ukrainian National Republic had borders which closely correspond to today. (Actually, parts of the Voronezh and Kursk regions were also included.)
A question I hope you're asking yourself is on what basis these demarcation lines (between Russia and Ukraine, and those other states) were made.
As a result large lands in the east which are ethnically and historically Russian became part of Ukraine.
I've disputed this Russian fairy tale so many times on the net it's getting annoying. Eastern and Southern Ukraine (minus Crimea of course) NEVER had a Russian majority. Kharkiv, Zaporizhia, Kherson, Dnipropetrovsk, Odesa in pre-revolution times had 70-75% Ukrainian composition. Even that same Donbas had a three quarter majority of Ukrainians.