The Soviet Union was a de jure federal entity, like the United States, and in theory composed of autonomous Republics. The largest of those is the Russian SFSR, however, there were also 14 other Soviet Socialist Republics within the federation such as Ukraine, Estonia and Latvia. Each Republic, including Russia, in theory has its own government. The difference between "Soviet" and "Russia" in this context is the difference between the Soviet federal government and the Russian Republican one.

Through most history power was concentrated in the Soviet federal government and Republican autonomy was somewhere between limited and fictitious depending on the time period. However during Gorbachev's reform period more emphasis was placed on the Russian Republican government, culminating in the election of Boris Yeltsin as Russian president and the Russian "declaration of sovereignty" in 1990. Proclaiming the supremacy of the Russian Republican government over the Soviet federal one. So the analogue here would be if California declares that it's state laws should override US federal laws.

The August coup was the takeover of the Soviet federal government by a cliche of....well, actually the Soviet government sans Gorbachev. It was opposed by Boris Yeltsin as Russian president, who rallied the citizens of Moscow to demonstrate against the coup. In the aftermath of the coup's failure, it was Boris Yeltsin who effectively engineered the dissolution of the Soviet Union in the Belavezha Accords. Under the accords, signed in secrecy, the leaders of the Ukrainian, Russian and Belarus Republics signed an agreement declaring the independence of their Republics and that the Soviet Union cease to exist. Gorbachev was forced to accept this fail accompli. The analogue here would be if the governors of something like 75% of US states were to present the president with a declaration that the union is dissolved and the US president has to accept.

The fall of the Soviet Union was in many ways due to a power grab by Boris Yeltsin against Gorbachev, by dissolving the federal government Yeltsin removed the one level of government which is theoretically supreme to his own position. Thus by doing so he became the head of an independent Russia.

A coup is an internal military take over attempt. BOTH sides will be of the same nationality, assuming there is no direct outside interference.

Gorbachev didn't want to leave. The ones that "wanted in", to take power, were another faction. But this is very simplistic, even if I could name those factions.

However I'm not a historian & I'll leave it to someone else to fill in the details & then perhaps I'll request my own clarifications.