Translation:Onze oma is sterker dan wij.
Officially that is incorrect. Comparative adjectives use subject pronouns in Dutch, as long as the pronoun is being compared with the subject (here the Grandma). See here: https://onzetaal.nl/taaladvies/advies/groter-dan-jou-jij
However, many native speakers do not follow this rule. It wouldn't surprise me if it would change in the near future.