For this case we can translate the sentence given as:
Juan and I ____________very sad about your accident.
We must complete the sentence with the most appropriate option.
We note that the sentence speaks of two people (the first person and a third person).
"Nos": It is relative to "Nosotros". It is used when the subject is the first person in the plural.
On the other hand, the first person in the plural of the present indicative of the verb "haber" is "hemos".
Finally, we know that sadness is a feeling, so the correct option is:
"hemos sentido"
ANswer:
Juan y yo nos hemos sentido muy tristes por tu accidente.
