Problem starting two postgresql clusters on the same host

I have created two postgresql clusters on the same host, which work
perfectly when started individually and manually. But when putting them on
start script, only one loads and the other fails. Any hint? My installation
is postgresql 14.1 on Slackware 15 and my rc.postgresql looks like this:

# Start PostgreSQL:
postgresql_start() {
if [ -x /data/apps/postgresql/pgsql141/bin/pg_ctl ]; then
su - postgres -c "/data/apps/postgresql/pgsql141/bin/pg_ctl -D
/data/apps/postgresql/pgsql141/data start &"
su - postgres -c "/data/apps/postgresql/pgsql141/bin/pg_ctl -o "-p 5433"
-D /data/apps/postgresql/pgsql141/data2 start & "
fi

####

Incidentally, when I change to postgres user and run the command of the
second cluster in a terminal it runs perfectly. Otherwise if I source it in
a terminal, be root or postgres user I get an error message:
pg_ctl: no operation specified

Thanks in advance
Ibrahim Shaame