I think Engels and Marx are very ethical in their approach.
Ethics is correct conduct, and the Marxist emphasis and priority on practice is an ethical priority.
However, Engels , Marx and Lenin did not want their ethics to be mixed up with the long history of hypocritical and phony moralism of ruling class religions , etc. Thus, Marxist ethicists have a special obligation not to get their ethical injunctions confused or simulated to the traditional ruling class forms, such as religion. I think it is positive that Andy Austin is focussed on practice on this thread. I have criticized him elsewhere for scholasticism, and his approach here is much more practice centered. For Marx and Engels, morality was something that was associated with correct social behavior that operated within a certain class of people.