What do you mean by "immediate family"? That usually means spouse, parents, children, and siblings. Sometimes also grandparents and grandchildren.

If you mean something like that then your proposal seems overly restrictive. I don't see any point in say the USGS not being able to hire a seismologist they want to hire because the seismologist can't convince his brother to sell his Microsoft stock and his adult daughter to get rid of her Apple stock. Nothing that seismologist would be able to working at USGS is going to influence those stocks, nor is his work going to provide him with any inside information.