There’s a marriage entry for a Dec Q 1932 Liverpool marriage of a John G Callow to a Charlotte Campbell. They had a son and a daughter. The son’s photo is on a Brazilian immigration document of 1958, viewable on this link:

www.familysearch.org/ark:/61903/3:1:33S7-9GTY-9MXR?i=114&cc=1932363

*******
Is there a family likeness to your grandmother (ie could she have been his half sibling ?)

Jean C