I am set to purchase these cards for travel for the 2 of us during 3 nights in Stockholm - public transit only... the option including attractions is far more than we will spend on individual tickets for museums, etc.

I see exactly how to purchase passes with the senior discount (more than 1/3 off), and also how to purchase for a "group" of two. But now, I've read conflicting advice on having each person purchase their own card for use on their own phone vs me just buying for both of us in one purchase and having both passes on my phone only. Warnings like "you'll be delayed by having to go to a manned gate," countered by "just scan your ticket and swipe to the next ticket and pass your phone back to the next person."

We plan to always travel together. Which strategy is "right"?

SL tickets are for trams and buses as well, which you will probably be using more often than the subway system, so it might not really matter all that much. Actually, I would use 2 phones. Just my personal preference.