Barcelona - Buying T-familiar with T-mobilitat?

Hey everyone, I'm visiting Barcelona soon with my family and trying to figure out the T-familiar ticket. I understand it's part of the new T-mobilitat system, and I've already downloaded the TMB app.

When I try to buy the T-familiar in the app, it's asking for a T-mobilitat card or suggesting I download another app. I'm a bit confused as a tourist.

So, my questions are:

1. Do I need to buy a physical T-mobilitat card before I can add it to my phone/app?
2. If I buy a physical card and load the T-familiar onto it, can we just use the physical card directly for travel?
3. Is the TMB app itself free to download, and does downloading it give us any free travel?

Any advice or step-by-step instructions from those who've navigated this as tourists would be hugely appreciated! Thanks so much!