Question 1
Why does everyone use usted, and why do forms of address matter so much?
Respeto, respect expressed through form, is load-bearing in many Mexican families, especially toward elders and professionals. Usted, titles, and surnames signal that you take the person seriously. Dropping to tú uninvited can read as condescension, and with an older patient it can quietly end the conversation's trust.
The safe default is the one this app teaches: usted, Señor or Señora with the surname, and let the patient set any change in register.