does all the assignee have to respond and then you decide on the least outcome?

or once the least possible outcome is received overall approval is stopped/cancelled and assignees that did not responded yet need not to respond anymore?

as well, what environment are you on? - that might have impact on solution design.

Yes all users must respond prior to deciding outcome. 

Also we are on nintex 2016 on prem.

have a look on following thread, it might help you

https://community.nintex.com/thread/15263-multiple-approvers-need-reply-from-all?commentID=56183#comment-56183 

I think you need to do something a little more manual here.

We did something similar where we used a request review action, sent it to all the approvers and all had to respond. In the task list we created a choice column that we placed on the task form, then, once all the approvers had responded we queried the task list for the tasks related to the item and then evaluated the values of choice column we had added to our task.

In your case, you could use a parallel branch and query the list for tasks related to that item and where the outcome is A in the first branch, B in the second branch and so forth. Then do a collection operation count on the values in each of the collections and that should tell you how many of each outcome you have and then the workflow can behave accordingly.