I have 2 sets of dates, and do not know which is right...
The Caesar allegedly arrived in Twofold Bay, NSW on 19 March 1855, and then sailed on to Port Jackson (Sydney) arriving on 29 March 1855. The Nuss family disembarked in Sydney I believe.
The alternative arrival date in Sydney is from the shipping arrivals/departures transcriptions and these state the Caesar arrived on April 17th, 1855.
Is this of help?