[...]
I am not (yet) posting the trigger code because this post is long already, and if your answers are 1) yes, 2) no and 3) triggers often work / fail like this, then there’s no point and we can wrap this up. But if not, I will happily post what I have. Thank you.
This is too much prose for the regular programmer, show us the code, and point out what doesn't work for you, then we can help:-)