One cannot see himself/herself in the dark.
When only the reflexive se is being used. the sentence.
no se puede ver en la oscuridad
means he/she cannot see himself/herself in the dark
When only the impersonal se is being used, the sentence,
no se puede ver en la oscuridad
means one cannot see in the dark.
However, I don't understand how to construct sentences when both the reflexive pronoun and the impersonal se is required.
likewise, I would translate sentences 2 and 3 in a similar manner which isn't the desired construction.
One should be happy with himself/herself.
One should judge himself/herself before judging others.