Read the section of your Wikipedia link covering Legality of civilian casualties. The deaths of two civilians who happened to be using Russia's bridge to occupied Crimea at the moment when that legitimate military target was attacked by Ukraine are unfortunate but are absolutely not a war crime.
Incidentally, what do you think about the wisdom of taking a family summer holiday in occupied enemy territory during a war? Any opinion? Would you advise it?
In my opinion, there are some legal arguments which seem to show that Crimea belongs to Ukraine, and there are some legal arguments which seem to show that Crimea belongs to Russia.
But the most fundamental argument, in my opinion, is the right to self-determination (
https://en.wikipedia.org/wiki/Self-determination ), which is mentioned in the U.N. Charter.
This is why Ukraine's battle may be a lost cause since 2014, particularly in a political context where the West has committed many crimes (Yugoslavia, Afghanistan, Iraq, Libya and so on).
The many Russians who take their vacations in Crimea are perhaps not much interested in politics, and they may watch Russian TV every day, which may shape their political opinions. Perhaps they go to Crimea because they can no longer go to Western Europe or Ukraine, or because it's less expensive than Sochi.
Ukraine's policies seem to be governed by a toxic nationalism: the leaders of Ukraine, probably with substantial support of the population, want their country large and powerful, they show very interest in what the locals think.
This kind of mentality has probably been very common throughout human history, but it must be fought, in my opinion.
