If you're flying in from North America on Friday, that day may be pretty much lost to jetlag and sleep deprivation, so I wouldn't plan one of the expensive modernista sites that day. Maybe walk around the Barri Gotic and, if still not brain-dead, the Eixample.
For architecture lovers, La Sagrada Familia and the Sant Pau modernista site would be great stops on Saturday for sure. You'll need to pre-book LSF to avoid an interminable ticket line. You'll probably want to include one of the towers for a close-up view of some of the architectural elements. So far, it has been possible simply to walk up to Sant Pau and buy your ticket on the spot, which will provde some much-needed flexibility.
Other important and worthwhile architecture-related sites include: Parc Guell, Casa Mila/La Pedrera, Casa Batllo and the Palau de la Musica Catalana. (There are others.) All require pre-purchased tickets because of the lines, and this will be a serious challenge for you because you have so little time. Who knows how long you'll be at each site? I'd say 90 minutes is about the minimum for most of them, but Sant Pau needs a bit more time and the Palau somewhat less. The Palau requires a tour, but English-language tours are very frequent and not terribly long.
Fortunately, I think a few of the sites sell slightly more expensive tickets that don't tie you to a specific entry time. I believe you'll need to take advantage of that if you want to try to squeeze in more than 3 sites.
Andorra la Vella was not an attractive town in 1972, and I gather that it resembles an outlet mall these days. I think your time would be better spent elsewhere. I don't know what route you're planning to take, but I enjoyed the lovely historic center of La Seu de Urgell when I visited it in 2016.
Edited to add: I should have mentioned that the top modernista sites in Barcelona--except for Sant Pau--are often very crowded. This is especially true of Casa Mila and Casa Batllo. If your husband really dislikes crowd scenes, it might be better to skip those two in particular. Parc Guell, being outdoors, doesn't feel so mobbed.