For the second part of your question, since you are using yb-ctl, the way to pass tserver gflags is:
./bin/yb-ctl start --tserver_flags "max_log_size=256"
For the second part of your question, since you are using yb-ctl, the way to pass tserver gflags is:
./bin/yb-ctl start --tserver_flags "max_log_size=256"