England to US... when??

Okay my Avery relatives arrived in New York in 1841. A similar family arrived in 1855. Did the same family return to England and come back or is it coincidental? Which is correct? Why are there no signs of them in the 1850 US Census? What if I'm wrong? I guess I won't be the first to report history incorrectly - maybe we'll accept it over time. I'm still thinking of erecting a monument of myself. In a few hundred years, people will believe I did something heroic, and maybe even generate a good story to support my feat.