Hi Peter, I have an family member with GC who visits the US for short periods of time every 6 months to maintain it. They currently have no intention of moving

Hi Peter, I have an family member with GC who visits the US for short periods of time every 6 months to maintain it. They currently have no intention of moving to the US. Recently, they seem to be getting more scrutiny at the airport due to the US not being their permanent residence. Is it possible for their GC to be revoked for this reason? If it is, then is there any way they can continue on with their lifestyle and still maintain their GC (by investing/buying a house/etc.)>