Another trick is to reduce the parent’s role strictly to managing the children. Spin-off the process of creating the %dataset and of determining the number of workers to a single child ... call it the project manager. The PM then informs the parent how many children are needed, and the parent spawns them. Worker processes can, say, ask the PM for another unit of work, which the PM doles-out and sends to them. There is also another child process which is the recipient and filer of completed work units.
Now, you have a dumb parent who has two gifted children (the PM and the filer), as well as a variable number of hired grunts. No large chunks of memory get duplicated on-fork, and that should eliminate your memory problem. The parent’s only job is to see to it that its children are alive. The children talk among themselves. Like any good bureaucrat, the parent is responsible for everything but basically does nothing . . . :-)