Can multiple users fill out the same form?

Rafael91 - the only way you could do this would be to have two different surveys. If you are using Forms Pro, you could then link the two surveys together with variables. Depending on who these people are, and where you have their information stored, you could link this all together and send an email to the 3rd party when the two questions from Survey 1 are complete.

You could then pass through those answers (if this makes sense for the 3rd party person to see them) and display them on Survey 2. The 3rd party person could then respond to the questions, then submit.

You could then have an email sent to you (or whomever needs the results) with all of the responses combined. 

You would need to A) use Forms Pro for the surveys, and B) use Power Automate for the triggers and linking everything together.