I do not know about a Vivian CROMER as being Floyd CROMER's sister. I have his siblings as being Floyd Franic CROMER born 4 May 1882, Grace CROMER born 17 Jul 1884, Elizabeth A. CROMER born 17 Jul 1885 and a Clyde CROMER born after 1885. This does not mean this information is accurate but it is from the CROMER family.
These were the children of William Harrison CROMER (1859-after 1937) and Elizabeth A. GROSVENOR (1857-after 1937)
Your Floyd and Vivian could have been a child of one of William Harrison CROMERS's siblings. I do not know how many of them went to Manistee, MI. When was your Vivian CROMER born and where?
I know that William Harrison CROMER had seven other siblings and they were the children of a Harrison CROMER and a Pheobe Ann GASKILL of Shelby County, OH.
As for when did they migrate to America -- before the Revolution. We know that William Harrison CROMERS's great-grandfather was Abraham CROMER born 1775 in VA.
My interest is only in the GROSVENOR family and Elizabeth A. GROSVENOR was my wife's great-grand aunt and younger sister of her great-grandfather, De. Alvah Whitney GROSVENOR (1856-1936) of Sidney, Shelby County, OH.