I will be meeting with my parents and their estate attorneys in the attorney's offices in a state in which I do not live. Can I expect truthful answers? In other words, can an attorney lie for the benefit of their client, or themselves?
Attorneys are universally required to tell the truth at all times and generally, they do. They are not allowed to lie on behalf of their clients or themselves.
This doesn't mean that someone else's attorney necessarily has your best interests at heart. And, attorneys can, for example, fail to mention options that exist, but might not be the best for the attorney's client.
Also, if an attorney's client lies to him or her about the facts, the attorney could conceivably say something inaccurate while believing it to be true.
In the kind of meeting you are describing, however, most likely, the attorneys are simply going to explain your parents' estate plan, over which you have no control or say in any case, and there is no reason for suspicion or paranoia.