I am assuming you are asking this with respect to O365 environment.
Regarding three-stage approval workflow: This can be easily replicated using the state-machine. Here is an official example of the same:
https://www.youtube.com/watch?v=-Wv7w9tKQ2I.
Regarding collect feedback workflow: I am not sure if we can replicate the classic 'Collect Feedback' workflow, as it is, in Nintex. But, you can give it a try using the state machine again.
For assigning the approvers for your workflow, you can create a variable of type 'Person or Group' and enable the 'Initiation' property for it. This would make the variable appear in the 'Start a task process' action's form.
I hope this helps you.
Also, in case you crack the solution for the classic 'Collect Feedback' workflow, please do share your solution here.
Thanks.