Complex sentence: There is also a 1936 obituary for one Francois Marcel Grateau, with dates matching those of the first-named Marcel Grateau: it is likely that they were all the same man.
Split into simpler sentences: There is also a 1936 obituary for one Francois Marcel Grateau, with dates matching those of the first-named Marcel Grateau. Given the dates, and the coincidence of names, it is quite possible that they were all the same man.