Fiat 124 Spider & Alfa Romeo Spider - Humans Riding in Back Seat?

I've been researching these two little roadsters. I understand that some years have back seats (shelf with a cushon and lapbelts?). Anybody here have experience fitting human beings in the back seat? I have a 5' 1" granny and 9 years and growing kid that I will need to stowe back there on occasion. I'm 5' 9", if that matters.

It seems there are no photos on the Internet showing actual use of the back seat in these machines. I did see one video on YouTube of a man recording from the back seat with a driver and passenger in the front but have no idea what his contortions might have looked like. He was inconsiderate in that regard.

And if my relatives cannot fit in a peppy little Italian drop top then what in the world am I supposed to start researching now? These two little cars look so awesome for their price. Anything similarly special with more room in the back that won't cost me more than $20K? Thank you all for your assistance in this matter!

Anecdotal "evidence" only, I'm afraid, but I did witness a friend bring two high-school-age boys from Port Hope, ON, to Litchfield, CT, in a 124 Spider for a debating competition, and then drive them back. That would have been a solid 8 or 9 hours each way, although I assume the passengers would have switched places from time to time. I didn't hear any protests from the kids – but then, they were on a road trip instead of stuck in class, so how much protesting were they going to do?

My grandma, may she rest in peace, was pretty rad, but I don’t see her enjoying the ride in the back of a convertible–cramped, lots of wind, etc. 

If you need room for four, go up a few sizes to something like a Mustang or intermediate GM?