Am I sinful for using things my husband brought from his work, given my ignorance of their unlawfulness, and am I a participant in the sin? What should I do to atone for it, given that it's impossible to return them?

There is no sin upon you for what occurred by your use of the unlawfully taken vessel, due to your ignorance of the prohibition of its use. Indeed, ignorance and forgetfulness remove sin. As for compensation, it is upon your husband to return its like, if found, otherwise its value on the day it was taken. It should be given to the entity from which it was taken, if possible; otherwise, it should be given as charity to the poor or spent on general Muslim welfare.