Judging by the style of clothing and hair I would place this photo on 1870-1880. I think you can definately rule out husband #3.
The smooth sholder area of the sleeve- the pleating of the bodice, the printed necktie on the gentleman, the center part in her hair, the neck scarf- all popular 1870-1875.
When was Eva born? This woman doesn't look especially young. Also what type of photo was it? Size? card? postcard? writing on the back?
A good book to have is Dating Old Photographs 1840-1929. My copy has paid for itself over and over again.