Problem using multiple pipes in a multiprocess program in python

I'm currently working on a project for university in which have to generate numbers and transfer them to other processes using Pipes in Python. I'm pretty new to Python and especially to interprocess comunication, so I don't know where my problem is exactly.

import os
import random


r, w = os.pipe()
r2, w2 = os.pipe()
r3, w3 = os.pipe()


pid = os.fork()

#Parentsprocess
if pid > 0:
    
    os.close(r)
    os.close(r2)
    
    random_num = []
    n = random.sample(range(1, 1000), 5)
    random_num.append(n)
    print(random_num)
    
    zahlenstring = "".join(str(x) for x in n)
    
    zahlen = bytes(zahlenstring,"utf-8" )
    print("bytes:", zahlen)
    print("Parent process writes:")
    
    os.write(w,zahlen)
    os.write(w2,zahlen)
    print("Written text:", zahlen.decode())


#Childprocess
else:
    os.close(w)
    print("\nChild process reads:")
    r = os.fdopen(r)
    zahlen = r.read()
    print("Zahlen:", zahlen)       
    file = open("file.txt", "w")            
    file.write(zahlen)                      

    
    pid2 = os.fork()
    #Parentsprocess
    if pid2 > 0:
        os.close(w2)
        r2 = os.fdopen(r2)
        verarbeiten = r2.read()
        print("Partents number 2")
        print(int(verarbeiten)-1000)
        os.close(r3)
        os.write(verarbeiten)



    #Childprocess
    else:
        os.close(w3)
        print("Child number 2")
        os.fdopen(r3)
        print(os.read(r3))

First I know my code is messy and definitely not perfect, because I'm pretty new to Python. So I'm sorry for that.

Now to my problem(s):

1.Normally a file would be created and the numbers from "zahlen" written into it. It also worked fine until I added the third pipe and wrote into it in the second parentsprocess, so the child can read from it. When I remove the third pipe and the code for it after the second fork, it also writes into the file again.

2.for some reason the number is written twice in a row into the file, although the code is only executed once and the number is also written and read individually in the pipe.

Could someone help me please.