According to Russian visa policies, citizens of mainland China and Hong Kong are eligible for a free 72-hour or 144-hour transit visa when entering Russia through certain border crossing points. However, if you want to stay longer than the allowed period or visit specific cities in Russia, you’ll need to apply for a regular tourist visa.
For your travel plans, it’s essential to note that Black River (Black Sea) ports are not eligible for these transit visas. Instead, you’ll likely need to enter Russia through land borders with China, Kazakhstan, Mongolia, or Belarus. Please check the Russian Federal Migration Service website for more information and potential requirements for visa applications.
Assuming your travel plans involve visiting other parts of Russia rather than just crossing the border at Black Sea ports, it would be best for you (as holders of mainland Chinese passports) to apply for a regular tourist visa in advance through the Russian Embassy or Consulate in China. Similarly, as holders of Hong Kong Special Administrative Region (SAR) documents, you may need to obtain a regular visa from the Russian Representative Office in Hong Kong.
For personalized guidance and up-to-date information on your specific travel plans, I recommend consulting with the relevant authorities, embassies, or consulates before booking your trip.