Marilla really wasn't at all bizarre back in the early 1800s. It was fairly common, and is the name of a main character in the famous "young adult" novel
Anne of Green Gables. It was originally a short form of Amarilla, a "Latinized" form of
Amaryllis.
If you will click on the linked names
Amaryllis and
Beulah, you will find the origins of those as explained in the name dictionary on this site.
Fidesta and Abriella are definitely much more unusual for the time period than Marilla and
Beulah are. It's almost midnight now where I am so I will try and see if I can track down something about them tomorrow.