What's the difference in meaning between these sentences?
I thought their meaning was the same, but I get the feeling it's not because of the particles.
These two have a major difference in meanings.
Either of two should bear the sin.
At least one of the two should bear the sin.
The latter sentence is very close to the sentence below:
And the following dictionary entry (quoted from デジタル大辞林) the best applies to でも in the latter sentence:
So it implies that the best choice is both bear the sin, but only one person is still better than no one bears.
Regarding the former sentence, both is not allowed as its subject is clearly 片方.