I'm a manager of a bank branch. We have a small staff of four tellers. Two are absolutely dead weight. One of them is 61 years old, has been on the job for over 8 years (almost three times as long as I have) and barely can keep up with the most basic functions of the job. She depends highly on everyone else to help her and we make special accommodations because she is so slow at everything. She existed in this position for a long time like this because everyone else could pick up the slack. Now the staff has been trimmed because of the economy and one of our newest tellers, who's been around almost 2 years, is basically functionally retarded. Now we have two out of four people who are just dead weight. One is too, old, fat, slow and apathetic to motivate and the other does not have the mentality to excel in this job. This is NOT a hard job. How do we fire them? What do we do with them? The branch is too busy to deal with this level incompetence.
My hands are pretty much tied. There's a hiring freeze and one employee is a "protected class".

Try to find out where they excel the most and have them concentrate just on that. That way the other tellers are getting help from these two and they can work on the things the other two suck at.

Document everything. First offer training. Then, put some new policies in place and increase your job expectations for each of the tellers. When any teller falls short of their expectations (makes an error, miscounts the drawer, too slow, etc) write them up. Have a policy that three write ups will mean that the employee will be terminated. Have all employees go to a meeting (even though meetings are usually a complete waste of time and a morale killer)where the new policies are discussed and have each employee sign off on a statement that they understand the policies. If you increase your expectations of all employees, they will either step up or fail dramatically.