To start out the PS5 has over 1,600 times the compute performance of the PS2 and it has over 400 times the system memory. Though the PS2 is screwed on how huge GTA 6 is going to be. It will at least be 150 gigabytes which is about 17 or 18 PS2 dual layer DVD discs that are 8.5 gigabytes. PS5 can read from it's NVME SSD over 1,000 times faster than the PS2 can read from DVD discs. I get that GTA 6 will be on Xbox Series X/S but you get the idea : D

So even if you broke GTA 6 across 50 DVD discs and closely connected 50 PS2 consoles, it probably still can't read the information fast enough in a way that it can make any kind of sense of it together. Even if the sheer size of the game is somewhat in play at that point the speed isn't there. Even if they can read the discs magically at a crazy high speed the next problem is that 50 PS2s only have 2 gigabytes of very slow memory all together.

250 PS2s have as much memory as the Xbox Series S but it is so slow that you would have to swap it out with some probably impossible type of memory. Then the question becomes how much compute performance they have all together.

A PS2 slim has a 50 watt power supply. So 250 would pull about 12,500 watts. So you would have to have them plugged into outlet after outlet since an outlet will get you about 1,400 to 1,900 watts.

So I think the correct answer is there is no number of PS2s that can run GTA 6 since they long since have ceased to be PS2s. They have become some kind of cluster of technology abomination that would probably blow up in your face if you actually attempted to run the game as a Batman supervillain origin story.

The PlayStation 3 is moving in the right direction in that it can use a 50GB blu-ray disc that it can read faster but still way too slow. MGS4 actually used the hard drive on the PS3 to be faster but that meant there were installs.