Next, tell them that there is another way in both languages to show possession or ownership: by using possessive adjectives to directly modify the noun. So we could say his bicycle or, looking back at our examples: his book, our car, our house and her cats.
Write the Spanish possessive adjectives on the board, in the six-box paradigm for the three singular and three plural gramamtical persons. Write mi/mis on the upper left, nuestro, nuestra, nuestros, nuestras to the right of that box. Below mi/mis, on the left, write tu/tus, and likewise to its right, the plural possessive adjectives corresponding to vosotros usage -- vuestro, vuestra, vuestros, vuestras. Below tu/tus, write su/sus and to its right su/sus again, beneath the vuestro, etc., forms.
The next step is critical. Ask them how to say my bicycle (mi bicicleta), and continue with the most intuitively easy forms, avoiding the nuestro, etc., and vuestro, etc. forms. Be sure to put in a plural or two: her cats is a good one. Point out that she is singular but that she owns more than one cat. Ask them why they think sus gatos is correct. Get them to recognize that mi/mis are adjectives. It can be an aha! moment.
Finally, they are ready to translate the examples about our house and our car -- nuestra casa and nuestro carro. Throw in our [female] friends (nuestros amigas) to show that the adjectives agree with the thing "owned" in terms of gender and number -- because they are adjectives like any other in that regard. The gender and number of the possessor is irrelevant.
Drills should do a quick pass off of simple phrases in English, using familiar nouns for the things possessed.