Multiple users to a ProcessInstance

Hi Bonita Community,
I have User group, What i need to dispose tasks for each user, when each one finish their tasks,
-he will be added to a list.
-if he negates his addition in the middle of his interaction, he will be not added.

in each of this cases, the task will be release to a next user, but for Interested/Disinterested users, will not appers this processTasks again.

I need a full code path orientation, i dont have BonitaBPM expertise and im a college volunteer and dont received any education in BonitaBPM from my superiors, Help me please.