Well, the Ukrainians consider themselves as Russians about the same as the Chinese consider themselves Japanese. In other words, the Ukrainians won't give up any more than the Chinese were willing to accept "co-prosperity" 80 years ago. Now, consider that.
Fine, that means we will just going to have to let them fight each other until one side come out victorious.
I personally thought that they are much similar to each other than Chinese are to Japanese. They do have the same religion and their language is much similar to each other than Chinese is to Japanese. But I guess it has less to do with similarities and differences and much more to do with self-identification.
I just thought that they should have a mechanism to de-escalate conflict. What happened 80 years ago to China and Japan is not normal, because China was both having internal strife and was hardly a true unified and function country (by today's standard, China was a Somalia-like fail state for decades). And China was an unindustrialized agricultural country with not arms industry, while Japan was an rising Asian new military industrial power. That imbalance of strength vs resources-under-title basically deprived the two from ever having a working method of de-escalation in the first half of 20th century.
But as soon as China got rid of its own internal problem of unification (administrative and bureaucratic structure) at 1949, and develop a decent enough Arms industry for self-defense a couple of decades after 1949, China and Japan were able to re-establish a working foreign relation, as well as mechanism for de-escalation, in the face of on-going territorial dispute between the two.
But Ukraine and Russia seems to have no such working mechanism.