The threat of traffic in an OCTA airfield would be briefed in the approach briefing during cruise. However a specific "plan" wouldn't exactly be detailed as the exact circumstances and relative positions aren't known would require differing actions. Generally should such traffic as you describe be encountered the plan would generally be see and avoid, separate ourselves vertically as well as horizontally, wait for said traffic to become clear (land or exit the circuit etc) and then proceed.
It is not a recommended practice to disable in anyway the TCAS functions for anything other than an engine failure where it is directed by the checklist due to the lack of performance requirements to comply with possible instructions, thus forcing another TCAS aircraft to comply with a resolution. I can't speak for ops overseas, but in Aus, it is not practice to turn off TCAS in anyway... what's the point in having it then?!?
Typically the thing that make things hard is a/c not making calls due to lower requirements these days and also perceived lack of need by the GA/smaller aircraft. Typically jets are doing 250knots from 30nm out which means they will enter the circuit (at approx 200knts) in around 7-9mins from that point. Things happen pretty quick and wider berths than expected are preferred as a result. We also want to prevent TCAS events (paperwork!) which are time based and whilst we know the parameters of such events, we don't see the exact real time limits/points that these will trigger.
The working environment is pretty busy as soon as you get a couple aircraft in the area. Crew co-ordination, configuration, ATC running on another radio at the same time giving traffic info, all the while trying to separate yourself from other aircraft. Add to this traffic magically appearing at 5nm-10nm without so much as a position report or response and it gets intense quickly. This has happened to me multiple times for varying reasons...
Earlier it was said that they "instructed" the go around as a last ditch effort, esp seeing as from their point of view (and my interpretation of the regs) they had right of way. This sounds about right and simply an extreme example. Typically anything we ask of another aircraft whilst trying to separate is a request more than an "instruction". Eg "if you could remain north of centreline until we depart south" is just us simply trying to ensure some sort of separation. It's hardly "ametuer atc".... it's professional pilots trying to ensure the safety of their aircraft with other pilots who may or may not be cognizant of our spacing requirements. Of course no aircraft is required to comply with any "request" and thats fine, we don't expect you to if you have right of way, so we'll typically just wait.
For the most part, despite my few bad experiences, usually GA/slower aircraft are more than helpful and usually more than willing to slow up/be # 2/give way etc etc and even usually offer it without us even requesting. I can tell you it's greatly appreciated and an absolute pleasure to share the airspace with you guys. I also understand that there are some situations which can be a pain for them and some of our guys push the friendship with straight in's onto rwy's with tailwind when other aircraft are using the reciprocal. I can't speak for all but personally will only try said jazz when it doesn't conflict with any known traffic in the area that has right of way.