What does it mean that the T-Familiar card is "shareable"? Can my whole family ride on a single ride? Or that we only need to purchase one card, but each person counts as a ride each time we travel?
The latter statement is correct.
The T familiar card is good for 8 journeys in a 30 day period and can be used by more than one person. That means that one person can take 8 one way trips, two people 4 trips, four people 2 trips, etc. You can purchase and reload the cards (if needed) at the Metro stations.
How many people in your family and approximately how many trips do you anticipate taking?
There were only two of us when we traveled last May, we weren't sure how many trips we would take, but between both of us we thought it would be more than 8, so we purchased two T-Casual cards (not shareable, but good until the "fare changes" so more than 30 days). Also can reload the cards if necessary at Metro stations. Ended up using 6-7 trips each. We were also able to use the T Casual Card for the Rodales R2 TRAIN from Sants rail station to Prat terminal 2 airport (can also use the T familiar card as well).
I found the zone designations a bit confusing, but it turned out that everything that we wanted to see was in zone 1.
It should be noted that neither the T casual or T familiar card can be used for the T2 METRO from Sants to Prat.
Thank you! That answered my question.