Don't know if this will be much help to you or not.I went to a subscription site I have and did a lookup there.I found the 2 marriages you mentioned, so I manually checked out this database for Thurman's married in Union Parish.There were only 5, I am attaching the other 3 below.I took note that all, with the exception of one, took place around the same time frame as those you mentioned.The exception took place 20ish years prior.Do you think we are looking at marriages of parents and later their children???
From"Louisiana, 1718-1925 Marriage Index"
Thurman, J. D. Spouse:Amanda Sanders Marriage Date:Aug 05, 1873 Location:Union
Thurman, John W. Spouse:Rosa Dison Marriage Date:Nov 18, 1897 Location:Union
Thurman, Robert M. Spouse:Deliah C. Ward Marriage Date:Jul 14, 1898 Location:Union