Docm's advice is about the distance between two villages.
Your target is to build one village and another one far enough from the first to be counted as another and not the same village.
As the distance of your villages is 75 and the minimal distance between villages needs to be at least radius+32 Blocks, while radius describes the distance between the first village's center and the furthest door of it, your villages shoul be far enough from another.
There are now two error sources:
Either you have got any door between these two "villages" which connects them to one large, or you are too standing too far away from the not-working platform.
In the first case, destroy the doors in the middle.
If you haven't got any doors in between these villages, just try to play/stand/run whatever between them.
Depending on the servers configuration there is a limit of blocks that may be between you and the mobs (usually about 60-80 blocks). If you are too far away the mobs chunk stops working. This means, the mobs are not running around, not spawning anything and for sure not breeding anymore.
So, to get your farm working properly, make sure that all chunks of the farm are loaded.
Which you may either achieve by being between them or putting one of your friends at he bottom spawn layer and yourself at the upper.
Depending on which plugins are installed on the Server there may be even a block or something called "chunk loader" but one of them at the bottom-spawn-area and your problem is solved.
Your villagers need a village to breed. A wooden door will only count as a house if one side of it is "outside", which is to say has nothing but air blocks above some block within 5 meters.
So you could fix this be building a chimney though the ocean above every door.
Best Answer
The distance of 64 is required between doors of different villages, not the villager entities. The distance is spherical, so it applies vertically as well - see the old DocM77 iron farm tutorial for example: