In the case of web and database users, they usually run as their own user. You can use the
-u flag to show only processes running as a certain user like this:
top -u mysql. You may also use the
-p flag with a comma separated list of PIDs you want to follow like this:
top -p 123,234,345.
You might also find
htop more useful in this situation. Besides the options above it has much more flexible display options including following selected items so you don't loose them in the list. Once you setup your columns and sort order, turn on tree mode and then follow the parent of the server you are interested in. All it's children should show up just under the cursor.