If you live in a war zone, occasionally you are going to come under fire from one side or the other. It's unfortunate but mistakes are made.
You do know don't you that the reason why there is a war zone is because Russia keeps invading. If Russia had kept out of Ukraine, everybody in that country would be living in peace side by side.
To your last point: "[t]he separation of a minority from the State of which it forms a part . . . can only be considered as an altogether exceptional solution, a last resort
when the State lacks either the will or the power to enact and apply just and effective guarantees." (The Aaland Islands Question: Report Submitted to the Council of the League of Nations by the Commission of Rapporteurs, League of Nations Doc. B7/21/68/106 (1921).) In 2014 the new government of Ukraine revoked Yanukovych's law passed two years earlier making Russian an official language in Donbass (iirc). Although this decision was vetoed by the new President, it triggered the demonstrations in Donetsk and Luhansk. The Oliver Stone film implies that the government somehow brought in ultra nationalists to turn the peaceful protests violent. The subsequent oppression in those regions (the so-called Anti terror operation) seems to me to meet the criterion of "the State lacking either the will or the power to enact and apply just and effective guarantees".
Googling "Ukrainian army uses civilians as human shield in Mariupol" brings up links to claims and counter-claims. Given the past history of the West's intelligence services I think it's best to treat what our one or another journalist, intelligence source or government says with caution. The point is that the right thing to do in a war is to evacuate civilians if possible. If people were prevented from leaving apartment blocks then this would be a war crime.
A while ago I came across a video called "
An interview with Scott Ritter". At 37 minutes he is asked to explain the legality of Russia's invasion. His answer lasts about 7 minutes I think, but he describes how Russia acted according to international law. Now I've just heard the Supreme Court say something about Scotland not being oppressed by the UK, and this makes sense of Scott's explanation about the legality of Donbas independence.
I also wanted to verify his claims earlier in the interview about the Maidan protests and subsequent events, and it appears he could have got his information from the Oliver Stone documentary, which details the interview with Yanukovych who explains the circumstances in which he had to decide whether to sign the treaty with the EU, and with Putin in which Putin says Russia "would not pay for Ukraine to sign up to the treaty" (in 2013). This clarifies that Russia was not putting undue pressure on Yanukovych, correct?
Anyway, I thought I'd post the link to the Ritter interview.