Multiple signs in Single form

Hello I am facing one problem , my client requirement is like that in unifier creator will initiate form and send it to multiple users. in which some activity done by one user , other activity done by other user, so how in unifier when i am sending form to   multiple user how i can validate that particular activity have access of particular user. how i can give access on the basis of data element .is it possible if not is there any workaround ? . or one more thing required how in single form on login basis user names