How can the difficulty set lower for my lower-hashing workers?
You should normally submit 5 to 10 shares per minute. Five minutes without a share and the stratum connection times out.
The pool should provide the instructions for choosing diff, either seperate ports or encoded in the password string.
Some will also use vardiff to automatically adjust the stratum diff, within limits, according to your hash rate. If you can't find shares
at minimum diff maybe try another pool that allows lower diff.