...Would you list it as three discreet 'waiting for' items on your lists?
Essentially, yes. However, I would create each of those actions as "follow-ups" linked to the project (which this sounds like since there are multiple steps to move it forward). More often than not, I need to stay right on-top of everyone to ensure nothing slips through the cracks and everything is handled in a prompt and timely fashion (i.e. significantly less time than the duration between weekly reviews).
However, yes, if each person's sign-off was required than you'd likely need to track those sign-offs in some fashion that are independent of each other (i.e. separate items).
Clarification: A "follow-up" to me, in my system, is an active form of a "waiting for" (i.e. I don't sit around "waiting for" things, especially if I can influence them). I, personally, still designate items as "waiting for" but only for things I cannot influence such as "Waiting for package to arrive from Acme Inc." or "Waiting for January 31 to begin reviewing documents needed to file taxes by February X. (there's an actual minimum early date folks can file)". I don't usually organize "Get Bob's approval on Acme RFP" as a "waiting for" because I often can/will need to follow-up on that request in a more rapid, active fashion rather than the passive style that "waiting for", to me, seems to be geared towards (granted these
should be seen during the "Reflect / Engage" steps as you're using your system so ...).