Why wouldn't you use a tag that would be clipped on their clothes at around the same level as the table edge, and then put a reader at every spot? You would only need a 10-20cm read distance, which is doable, and you would meet the separation criteria so that you don't run into the issue of multiple tags in the same field.
The 125kHz tags and readers seem to have this range and it appears that you can even tune it up or down a little by using differnt sized antenas.
From what I have read, I agree with the idea that it will be difficult/expensive to read multiple tags with one reader.
That is maybe a good way. I road that it is possible to use only one reader with multiple antenas. So I need one reader and 4 or 8 antenas with a multiplexer.
Do you know a rfid reader which works good with arduino?
I think 10-15cm is fine.
And with one reader i do not disrupt the other readers