Translation:Nos encanta aquel piano grande.
Why not 'encantamos'
Because encantar works in the same way as gustar and the conjugation follows the subject, which here is piano. Thus encantar needs to be conjugated as the 'it' form - encanta.
More here: https://studyspanish.com/grammar/lessons/gustar
Nos "encatamos" aquel piano grande. sounds bad in spanish and is wrong because "encantamos" it mean enchantment in spanish.
What is the difference between aquel and aquella