He is a good father -> They are good fathers.
She is an excellent doctor -> They are excellent doctors.
Peter is a good brother -> They are good brothers.
She is an American singer -> They are American singers.
It is an english book -> They are english books.
I am a tall boy -> We are tall boys.
My father is an engineer -> Our fathers are engineers.
That car is very fast -> Those cars are very fast.
That toy is expensive -> Those toys are expensive.
The ball is new -> The balls are new.
*NOTA: Recuerda que en inglés los adjetivos no tienen ni género ni número, excepto los de cantidad y los demostrativos.
Demostrativos:
Singular Plural
That ---> those
This ----> these
~Espero que te sirva :)