The problem is how you precieve what together is. Also your question is A or Z. The reality is, monitors, all monitors do not work in the way WE(most keepers) think. They use A all the way to Z, with the middle areas being the most common.
The point is, we are working with individuals and these individuals have their own individual experiences and behaviors. Not all people get along and we are really dang social. Native tribes are very very social, yet different tribes fight to the death. in fact, modern civilized social folks are bombing the dog beans out of eachother. And domestic abuse is clogging up the court systems.
What this means is, in order to breed varanids in captivity, you must place two in the same cage for a period of times. End of that story. And like any other social(or non social) animal, the longer apart, the harder it is to put them together. This is similar with mice, rats crickets, what have you. Keep them apart and they fight when put in with new animals(people too)
In my experience and its a lot of experience(many world firsts or close) My task is to create conditions that allow for bonding of pairs or groups. If done right, they can be kept together without problem and with lots and lots of benefits(extreme success) Males even help nest and guard the nests. Also they protect the female. That is the goal of bonding. If there are other problems, Those problems determine the degree of bonding. And they can have no problems to killing eachother. Such is behavior. They are not windup toys. You cannot wind them up and off they go with total success, THESE ARE VARANIDS and as such, have resisted such an approach.
As with any goal, there are always roadblocks, that is, things that get in the way of success. Again our job is not to react in a extreme way to roadblocks, but treat them as things to overcome.
So back to your question. Prasinus are one of the most tolerate varanids to keep together. But they can have problems. These problems are normally associated with bad experiences the individual monitors have had.
Hatchlings of any species can be raised together and will naturally(all on their own) form bonds with other individuals. This also means, their may be individuals they do not bond with. Its behavior, not biological function.
The older they are, the less chance of this happening. But it still can happen. You can get an old male and an old female and they will get along like they knew eachother their whole lifes. Thank god for this or we would be screwed.
So do not think of it as a yes or no type of question. the person bought a group so they could breed them, then you have to think of them as a BREEDING GROUP. Your task as a keeper is to allow them to be a breeding group. Not seperate them into a non breeding group. Sure is simple huh?
When you put any two animals together that are unknown to eachother, they will have a period of adjustment. This includes fighting. But should not include the killing of the others. Like any other animal, "fighting" is a way to establish ground rules. They must be allowed to do this. For newbies, this part is really hard.
So if you want to breed them, put them together and see if it works, if it doesn't work, then move to B, take the next step, if that does not work, move to C, if that does not work, move to D, etc etc. Sometimes you move from D back to A, its not a direct line to Z.
But to say, together or apart is very naive and has not worked in the past. Keeping monitors in breeding groups has worked to a level that is hard to believe. Keeping them seperate has not had a good history.
Now to another point, why did the person pick such a species like prasinus, which do not have a good history of captive success to start with. Yes, they are no different then any other species, but they are less tolerate to abuse, as in, they are skinny and have less reserves to hold them through bad choices their keepers make. In other words, they are a poor choice for a beginer when it comes to breeding varanids. They are a good choice once you learn what monitors actually do.
In the meantime more prasinus are killed by keepers thinking they are up to the challange. Which is sad as the monitors don't want to die because of operator error. Cheers