Have you searched the 1920 and 1930 census for them? That would be my first thing to do.
The second to try to get a copy of the book "LaSalle Parish History, Families Past and Present". The LaSalle Parish Library did have some copies for sale. If no more are available, they do have a copy there, you may ask your local library to get a copy if they don't have one already. I looked through my copy for Rosa Russell and Rosa Rawlins but did not find her. The surnames are mentioned and may give you clues as to where to go from there. It is a great book for back ground and understanding how our families lived in the early days of Louisiana into the mid 1900's. If I had a scanner I'd make copies of the pages that mention your names, but I don't have one right now.
I'm sure the Library there will be happy to help you. I've visted the court house and library and found them all to be very helpful.
I hope this helps at least a tiny bit.