My parents come with 2x50lb bags and leave with 4x 50lb bags and 2 carry-on bags. They visit from Australia and many things are cheaper here, even with the Australian dollar weak against the US dollar - it's economies of scale as Australia's population is much smaller and many things are imported. So, they come and shop until they drop and take things back. They actual need to bring less with them as they always buy some clothes, new tennis shoes etc.
But it's only 2 trips to the airport a year. It will work if we only have 3 people for airport drives so a captain's chair can also be down. Or maybe roof racks. Or we just take 2 cars for all the gear. And while I complain about all their things, we're visiting them next month and taking 2x 40 lb scuba bags, 1 suitcase and 3 carry-on backpacks, so they normally bring 2 cars to pick us up - Dad's pick-up for the luggage and the Honda Civic for the passengers. Again, it's a once a year thing, so totally manageable.