Nope. One pipe is one pipe, for a chain of 10 processes you need 9 pipes.

Not sure what you mean by "adjusting the FD". FD 6 isn't "pipe number 6", it just happens to be the sixth file your process opened. Add two to it and the kernel won't give you pipe number seven, just say "What?"

Or worse -- maybe there really does happen to be an FD 8. You just spun the roulette wheel and landed on a number your process opened already. What is it? Who knows, but whatever it is, you're reading it.

6 is just a number, perhaps the 6th file your process happened to open, it doesn't mean "pipe number 6". Closing #6 doesn't close everyone else's #6.

It's completely okay to have the same file open and used in many different processes, too -- that's how shells work. When you run echo a or cat, they receive copies of the shell's own open file descriptors. That's what fork() does -- creates an almost-perfect clone of the parent, right down to memory and open files. Then they run exec() to become a different program, but keep the same open files.

So echo, cat, et all don't have to tell the shell to write to the terminal -- they do so direct.

Pipes obviously know to wait until the process writing to them finishes before saying they're done. That works for more than one process too. If you have two processes with copies of the write-end and one process with the read end, the kernel will wait for both write ends to close before the pipe gives up -- even if you just left that one open by accident. The same logic goes for the read-end.

Every process is independent. Close everything you don't need. fork() clones a new, independent process. Each process is its own separate little universe and the only thing linking it with any other is sockets, files, pipes, and/or mapped memory.

Threads are something else entirely. When you create a thread it works in the same process, literally sharing all the same memory, all the same files. Change it in one thread and it changes in all of them. That's why threads can be so tricky -- it's easy to rip the floor out from under your threads by altering something they're using simultaneously.