It turns out that in my case, simply replacing:

cd /to_some_file/ && nohup python3 run_process_1.py > /dev/null 2>&1 &

by:

cd /to_some_file/
nohup python3 run_process_1.py > /dev/null 2>&1 &

for the two processes solves the issue: the bash script now correctly terminates as expected.