I was marked wrong for ההצלחה שלהן זאת ההצלחה שלנו. Is it wrong, or just deficient programming on Duo's part?
It is much more convenient to use pronominal suffixes here instead of full pronouns.
הצלחתם היא הצלחתנו?
I don't know about convenience, it is not common to use possessive suffixes like this in modern Hebrew.