user20943: If a family member has been dishonest with me, and upon discussing the issue denies the lie, what is the best action?

user16489: Everything that happens to us is caused by an action we have committed in the sansara. This was common to Buddha as well (Devdatta's actions etc.).
Therefore the answer to the question What is the best action? is,
Understand that this is a result of an action you have committed in the past (maybe in previous births). Further, try to spread metta (kindness, love) towards him though he is lying to you. In future, he will admit what he did today. Until that there's no much meaningful thing to do.

user20675: Welcome, Lineke! I don't think that there is a straightforward answer, as I think the situation deserves some analysis. I do not claim that this is the "best" action; I am only using what I've learned from a few Suttas as a guideline, so I would encourage you to read more on the matter.
First, I will assume that you know for sure that you are being lied to. Second, I am assuming that, when this other person lies to you, you feel hurt, or angry, or betrayed, or it causes you to suffer in some other way (I am assuming this, because falling into this kind of distress is only human, as we all know from first-hand experience). Now, with those two assumptions in mind, I put forward that the problem has two elements: the harm the person is causing themselves by lying, and the harm that they are causing you with their actions. Please bear with me, as I think that addressing the first is important to be able to address the second part.
Regarding the first part, the Buddha taught that we are all heirs to our actions, and have to live with the results, good or bath, whether in this life or the next. This means that the person lying is generating bad results for themselves. At the very least, they'll have to live with the lie weighing on their conscience and, depending on whether one adopts the view of rebirth, they aren't helping themselves to secure a good future life.
Now, addressing the second part, a relevant Sutta that touches on how to react when one is being harmed is MN 21. In it, the Buddha explains that if a group of bandits should capture someone, and savagely cut them up, limb by limb, even then that person should cultivate feelings of goodwill towards the bandits. Extreme though that simile may be, it illustrates an important point about what the Buddha thought a good strategy for dealing with harm is—namely, to cultivate goodwill towards everybody, regardless of whether they are being harmful to you or not. Now, as a lay practitioner, who is as human as anyone else who is not an Arahant, I know this is incredibly difficult, and perhaps you'll realize that in order to cultivate goodwill, you will have to let go of a few things.
If you find that cultivating goodwill for that person is too hard, then perhaps you can weather the issue with compassion, or equanimity. When one considers that the person lying is causing harm to themselves, one can maybe begin to feel a little compassion for them. If one understands that the harm they are causing themselves will only make their life worse, one can begin to feel genuine concern for their wellbeing, and not in a condescending kind of way. This is, in fact, one of the strategies the Buddha taught for dealing with feelings of animosity toward another. If, when you feel anger, or hurt, or betrayal when you're lied to, perhaps remembering that the person doing the lying is harming themselves will help you let go of that suffering and develop more wholesome feelings instead.
I hope this is helpful. With Metta.

20943: <p>If a family member has been dishonest with me, and upon discussing the issue denies the lie, what is the best action?</p>
 16489: <p>Everything that happens to us is caused by an action we have committed in the <code>sansara</code>. This was common to <code>Buddha</code> as well (<code>Devdatta's</code> actions etc.).</p>
<p>Therefore the answer to the question <code>What is the best action?</code> is,
Understand that this is a result of an action you have committed in the past (maybe in previous births). Further, try to spread <code>metta (kindness, love)</code> towards him though he is lying to you. In future, he will admit what he did today. Until that there's no much meaningful thing to do.</p>
 20675: <p>Welcome, Lineke! I don't think that there is a straightforward answer, as I think the situation deserves some analysis. I do not claim that this is the &quot;best&quot; action; I am only using what I've learned from a few Suttas as a guideline, so I would encourage you to <a href="https://www.accesstoinsight.org/index-subject.html" rel="nofollow noreferrer">read more on the matter</a>.</p>
<p>First, I will assume that you know <em>for sure</em> that you are being lied to. Second, I am assuming that, when this other person lies to you, you feel hurt, or angry, or betrayed, or it causes you to suffer in some other way (I am assuming this, because falling into this kind of distress is only human, as we all know from first-hand experience). Now, with those two assumptions in mind, I put forward that the problem has two elements: the harm the person is causing themselves by lying, and the harm that they are causing you with their actions. Please bear with me, as I think that addressing the first is important to be able to address the second part.</p>
<p>Regarding the first part, the Buddha <a href="https://www.dhammatalks.org/suttas/AN/AN5_57.html" rel="nofollow noreferrer">taught that we are all heirs to our actions</a>, and have to live with the results, good or bath, whether in this life or the next. This means that the person lying is generating bad results for themselves. At the very least, they'll have to live with the lie weighing on their conscience and, depending on whether one adopts the view of rebirth, they aren't helping themselves to secure a good future life.</p>
<p>Now, addressing the second part, a relevant Sutta that touches on how to react when one is being harmed is <a href="https://www.dhammatalks.org/suttas/MN/MN21.html" rel="nofollow noreferrer">MN 21</a>. In it, the Buddha explains that if a group of bandits should capture someone, and savagely cut them up, limb by limb, even then that person should cultivate feelings of goodwill towards the bandits. Extreme though that simile may be, it illustrates an important point about what the Buddha thought a good strategy for dealing with harm is—namely, to cultivate goodwill towards everybody, regardless of whether they are being harmful to you or not. Now, as a lay practitioner, who is as human as anyone else who is not an Arahant, I know this is incredibly difficult, and perhaps you'll realize that in order to cultivate goodwill, you will have to let go of a few things.</p>
<p>If you find that cultivating goodwill for that person is too hard, then perhaps you can weather the issue with compassion, or equanimity. When one considers that the person lying is causing harm to themselves, one can maybe begin to feel a little compassion for them. If one understands that the harm they are causing themselves will only make their life worse, one can begin to feel genuine concern for their wellbeing, and not in a condescending kind of way. This is, in fact, <a href="https://www.dhammatalks.org/suttas/AN/AN5_161.html" rel="nofollow noreferrer">one of the strategies the Buddha taught</a> for dealing with feelings of animosity toward another. If, when you feel anger, or hurt, or betrayal when you're lied to, perhaps remembering that the person doing the lying is harming themselves will help you let go of that suffering and develop more wholesome feelings instead.</p>
<p>I hope this is helpful. With Metta.</p>
