You should examine why you chose Ukraine as an example here rather than Palestine.

They aren't complete non-violence. They support every single bit of violence enacted against those they deem undesirable, whether it is at home or abroad.

They oppose violence by proletarians. They support violence by the bourgeoisie. It's as simple as that. They pretend this is non-violence when in reality it is just anti-proletarian.

Christopher Caudwell's book Studies In A Dying Culture and the chapter on Pacifism is really good and discusses this.

There is not much left of importance in bourgeois ethics. Chastity, sobriety, salvation and cleanliness have ceased to be topics on which the bourgeois feels very deeply. There is, in fact, only one issue on which the bourgeois conscience is to-day warmed into activity. Pacifism, always latent in the bourgeois creed, has now crystallised out as almost the only emotionally-charged belief left in Protestant Christianity or in its analogue, bourgeois ‘idealism’.

I call it a distinctively bourgeois doctrine, because I mean by pacifism, not the love of peace as a good to be secured by a definite form of action, but the belief that any form of social constraint of others or any violent action is in itself wrong, and that violence such as war must be passively resisted because to use violence to end violence would be logically self-contradictory. I oppose pacifism in this sense to the Communist belief that the only way to secure peace is by a revolutionary change in the social system, and that ruling classes resist revolution violently and must therefore be overthrown by force.

But modern war is also distinctively bourgeois. Struggles such as the last war arise from the unequal Imperialist development of the bourgeois powers, and earlier wars of bourgeois culture were also fought for aims characteristic of bourgeois economy or, like the wars of the infant Dutch republic, represented the struggles of the growing bourgeois class against feudal forces. In its last stage of Fascism, when capitalism, throwing off the democratic forms which no longer serve its purpose, rules with open violence, bourgeois culture is also seen as aggressively militant. Are we Marxists then simply using labels indiscriminately when we class as characteristically bourgeois, both militancy and pacifism, meekness and violence?

No, we are not doing so, if we can show that we call bourgeois not all war and not all pacifism but only certain types of violence, and only certain types of non-violence; and if, further, we can show how the one fundamental bourgeois position generates both these apparently opposed viewpoints. We did the same thing when we showed that two philosophies which are apparently completely opposed – mechanical materialism and idealism – were both characteristically bourgeois, and both generated by the one bourgeois assumption.

https://www.marxists.org/archive/caudwell/1935/pacifism-violence.htm

Should they just give up?

Go there yourself or shut the fuck up. Who are you to insist that the people of another country futilely fight to the last man from the comfort of your home? Go fight.