From Bergen to USA August 1887

I find my relative Anne Petrine Rasmusdatter Ytrehovde(age21, born 1866) in the emigrant protocol on August 11 1887. (Her first name is written Hanna). She is together with 6 others from the same county, Volden. They are: Elias Pettersen Velle, age 18 born 1869 Lars Gundersen Rebbestad, age 20 born 1867 Carl Thorsen Foldestad, age 23 born 1864 John Sivertsen Foldestad, age 24 born 1863 Anna Stensdatter Velle, age 21 born 1866 Jensine Andersdatter Velle, age 22 born 1865 The Inman line is noted behind their names. In the passangerlists available on Ancestry.com I find the four last ones Carl, John, Anna and Jensine arriving in Boston on the 27 August with Catalonia, which is owned by Cunard, not Inman. The 3 others I find no trace of in the passangerlists. S/S Ohio, owned by Inman, arrived in New York on the 27th of August, but no match to any of the 3 others. Nor are there any match searching the passenger lists on Ancestry.com. Anyone can advice me on this: Why would some go with Cunard ship, if they already had ticket with Inman? Since it seems that the 7 split up, what would be the alternatives for 3 unknown? Where would you advice me to search? I am amazed over all the information I have found on this internetpage.