Belarus is a Russian puppet state, not a Ukraine ally or member of NATO. Some of the forces the Russians invaded with came from Belarus
Any NATO forces in Ukraine are fair game. Any forces targeting NATO forces in Ukraine are fair game back. Only Ukrainians should be targeting Russians outside of Ukraine, IMO, but I don’t know that that is what’s going on in Russia or Belarus.
Yup. You are correct. Substitute any of the other, more NATO-oriented, countries in that region.