Except Donbas and some smaller areas, many of these places under siege have native Ukrainians in the majority, even though there are sizable native Russians around. The opinions of both groups should easily diverge. And the opinion of the weaker group can easily be dismissed when rifles get involved.
No, they don't. That's the thing. Even the Russian-speakers in Ukraine are revolted by Russia's action.
Also there's no such thing as "native Ukrainian" vs "native Russian" because Ukraine is a country with a civic definition of nationality, not an ethnic one. You're Ukrainian if you're a citizen of Ukraine. It doesn't matter whether your family originated from Ukraine, Russia, or Uganda: citizenship is nationality; nationality is citizenship. (This is a difference from Russia.)
Let's just safely admit that most civilians will be hiding in tunnels and basements rather than be fighting at all. A more responsible govt would have allowed rapid evacuation of the main eastern cities towards western Ukraine.
Fronline combat is just a tiny, tiny part of the war effort. In a modern, professional western army, you've got like 8 or 9 non-combat military job for every single combatant. The rest is logistics, medical, logistics, technical, logistics, intelligence, logistics, administrative, and logistics, with a dash of logistics and some additional logistics for good measure. Combatants need food, they need medical care, they need supplies, they need intel, they need communication and coordination. All these non-combat tasks can be accomplished by non-combatants.
This is what happens in every guerilla. In every insurgency. In every resistance. And this is the kind of war Ukraine is fighting.
Civilians are also good at psy-ops. In some of the cities and towns that Russia managed to seize, there were constant protests against their presence. Not fighting. Just people standing on the streets with signs, shouting slogans. No weapon or violence. Seems pointless, but it demoralizes the Russian troops.