My family does have an arrangement that could (and should, IMO) be used in other companies:
- What happens at work is work
- Conversely, when not-work time comes around, minimal mention of work is made

So, a twist of "What happens in Vegas, stays in Vegas". The family business has employed most (if not all) of my aunts and uncles over the years, yet work discussion at family parties doesn't go further than "How's business?" "Good. And how's your job going?". Any work-related intervention that may need larger explanations (e.g. when my father knew he would eventually die of cancer and decided to cede his parts to his brother) happens at separate times, in a family meeting called for that specific reason.

So:
- At work, you should act as you would with any other colleague.
- Outside of work, you should act as you would if didn't work together (unless said friend or family member expressly tells you they want/need to talk about work, but that should be the exception, not the norm)