The current government that was voted into power in a general election a few months ago, that was recognized as free, is considered the legal and legitimate power of the Ukrainian state by every nation in the world. Including Russia. The government was voted in trough legal terms (elections), so it's legal. In fact, they even left open the constituency seats of the occupied districts. That's how good they're following the rules.
Every nation in the world excluding Russia and its vassal states (and Afghanistan) also recognize Ukraine's sovereignty over the Crimea, and every nation in the world, including Russia but excluding South Ossetia and Abkhazia, recognizes Ukraine's ultimate sovereignty over the Luhansk and Donetsk oblast. It may have escaped your notice, but the official Russian point of view is still that there should be a ceasefire and preferably some sort of decentralization within Ukraine.
So it stands 194 nations saying Ukraine and the current government is the legitimate power in all of Ukraine, versus two unrecognized countries saying the separatists hold sovereignty over the Donbass region. Legitimacy comes from how many other people say it is, and thus how many people treat you as the sovereign of the state, so the government is also legitimate.
So your statement 'But the government is not legal nor legitimate' really has no valid ground. At all.
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