"Mon beau-frère gagne autant que sa femme."
Translation:My brother-in-law earns as much as his wife.
Next time, please think before you use a pronoun instead of an adjective before a noun.
"Ça" is short for "cela", meaning "that thing there". It is a pronoun and can be used as a subject or object, never to modify a noun.
Now, this is what you wrote: "my brother in law earns as much as that thing there wife".
There are many homophones in French but they are never interchangeable.
"Sa" is the possessive adjective you need to translate "his wife" = sa femme.