I think the information about Isak Goldberg simply comes from his son baring the middle name Isakovich. Meaning that he is the son of Isak.
His son is known as Nikolai (Israel Nison) Isakovich Goldberg-Rudkowsky.
There is a Nisson Goldberg Rudkovsky on this ship manifest with his a lady who might be his wife Bertha. Apparently, they had Finish nationality but he was born in Vilnus, Lithuania. https://www.familysearch.org/ark:/61903/3:1:33S7-95H7-P9Z?cc=1923888
Who do you think Isak is the brother of?