What do you do when you can tell that someone's stories about why they're behind on work and taking multiple leaves is total BS? I so badly want to call this one person out for lying about a family emergency ... I saw a photo of her on a holiday through a common friend's Instagram, but don't want to present it as evidence because I'm going to come off as nosy/invasive. What would you do? Let it be or bring it up?

Leave it alone.

If they have enough PTOs and decided to take them, I think it’s best to leave it alone even if they lied.

I would be more worried about why this team member felt like they needed to lie in the first place. Could it be that your team is scared of asking for leaves and feel like the only way they could do so is to fake a family emergency?

I wouldn’t focus at all on the why. It does not matter. I would focus on the impact to the client, the business, and the team of falling behind. I would look for short term solutions on how to solve the immediate needs and then follow up and collaborate on strategies for staying caught up long term. As hard as it is not to judge people’s decisions on how they spend their time, it is simply out of your control. Focus on what you expect them to deliver.

A previous report did this. Said she and her whole family were sick for a couple of days. She said all she could do was stay in bed — couldn’t even check messages. She posted pics of herself on social at the Christmas tree farm. I never called her on it, but trust was broken. I instead dealt with her performance issues in other ways.

I'd leave it alone. If the behavior is consistent, consider having a conversation with this person for sure.

I also want to remind you that just because there is a photo of a family holiday does not negate a family emergency. It is imporant to take time to appricate family and celebrate, espically in hard times. Here is an example for you from my own recent history (and no this isn't me in the story-everyone knows I did this on my time-I have a very safe working environment):
I took time off in January to handle the affiars of a recently deceased family member who I had been taking care of (Cancer). A friend of mine made the journey with me. A lot was done. The only photographs? The two of us taking a break to go skiiing. This doesn't negate all the work we did- it was a small break to breath and remember to live even in the hard times. A photo doesn't show everything.

Instead of directly confronting this person, maybe you could address it in a group and express your concerns about 'shady behavior' or 'dishonesty' more subtly. Later you could have a private conversation with them, so you seem like you're just offering your support and asking if they need help managing their workload. It's a more constructive conversation and it'll allow them to share their situation without feeling attacked... if at all they decide to.

Send the link anonymously to HR and their manager 🤣
But as Director of HR, just leave it. That’s my advice.

I wouldn’t call them out. But results speak for themselves. If they are underperforming, chances are, it will be noticed and consequences will be implemented.

It’s no one’s business why someone is taking PTO and they don’t owe anyone the truth. But if they are taking advantage of the system and it’s causing their work to suffer and the business to suffer, then that’s a problem that should be addressed. Keep it about business. Don’t make it personal.

If someone does not feel psychologically safe in the workplace to say why they are taking multiple leaves, it is most likely that they are burnt out or do not trust their management (or both). I would look at the overall culture and see where the failings are.
Some of the below comments will only futher exasperate the situation. Remember to not take the personal lives of others personally- they're our colleagues, not our friends, and they don't owe us the details of their leave time.