Honestly, no one can really answer this strategy quesion without having carefully read and analyzed the complaint, and without knowing the client's ultimate goals. Whether to file a demurrer and/or motion to strike instead of an answer or general denial also depends upon the judicial officer that would be hearing the demurrer or motion. Moreover, the response to your question also depends upon whether the complaint is verified or not verified. In short, there are many factors which go into deciding how to defend a lawsuit.
Only your own lawyer who's reviewed the pleading and spoken to you about the situation can answer this question, since there's no "one-sized-fits-all" answer.
For example, if you're not currently the executor, but the plainitffs have alleged that you are, it will cost you quite a bit to prove you're not, and if you ultimately are appointed executor, you'll have just wasted time and money arguing that issue, and they'll just re-file their suit against you.
Does the agreement in didspute have an attorney's fee clause? If so, that makes it easier for them and for you to hire a lawyer, since it ups the ante.
See a lawyer to have your documents reviewed and your facts disclosed.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.
The answer to your question depends on the facts of the case, including the desired result, budget involved and whether there is any way to resolve this dispute by negotiation or some settlement. You need to consult an attorney and discuss the specific facts and documents involved so that they can formulate a strategy that works for you.
This answer does not create an attorney client relationship. Consult an attorney before you decide on a course of action. A review of all documents and a consultation at a minimum is necessary to render effective legal advice.