I just found my Lyndie and Dora Brennan on the 1930 New York Manhatton census immigrated 1929
Living in the same apartment block is Andrew and Bridget Mulhall both aged 20 from Irish Free State. Immigrated 1929.
Also living in same block William 24 and Rosana 23 Martin from Irish Free State immigrated 1929.
As they all arrived at the same time, all could have made the crossing together, may have been friends or relatives.
I do have a little more info if it could help.
Contact me email@example.com