You could deliver them to the clients, if you can find them. This is one good reason not to hang onto original documents!
*** LEGAL DISCLAIMER I am licensed to practice law in the State of Michigan and have offices in Wayne and Ingham Counties. My practice is focused in the areas of estate planning and probate administration. I am ethically required to state that the above answer does not create an attorney/client relationship. These responses should be considered general legal education and are intended to provide general information about the question asked. Frequently, the question does not include important facts that, if known, could significantly change the answer. Information provided on this site should not be used as a substitute for competent legal advice from a licensed attorney that practices in your state. The law changes frequently and varies from state to state. If I refer to your state's laws, you should not rely on what I say; I just did a quick Internet search and found something that looked relevant that I hoped you would find helpful. You should verify and confirm any information provided with an attorney licensed in your state.
If you are concerned about the ethical aspect, the WA State Bar Association will provide an opinion as to what your ethical duty may be. The WSBA is at www.wsba.org .
Check with Bar to see if you can write letter and give them a deadline to pick up their documents or they will be destroyed.
In the future-have client sign a client agreement that you are not expected to keep copies after a certain number of years.
The answer given does not imply that an attorney-client relationship has been established and your best course of action is to have legal representation in this matter.