Congrats! I’m the fourth kid in my family so I have a real fondness for fourth-borns 
I also have a Beatles name (Molly) so I really like your names!
From your list I like Ruby the most - and the Beatles song Ruby Baby would be the best lullaby for her! - though maybe the Lucy similarity is a bit much. That all depends on taste, and if it doesn’t bother you, it doesn’t bother me!
Other Beatles-inspired names:
Willow (post-Beatles McCartney - Little Willow - goes well with the nature name Skye)
Calla (I was trying to think of any other girl names you could pull from Lucy In The Sky…, and I was thinking of the girl with kaleidoscope eyes. Both Calla and the beginning of Kaleidoscope come from the Greek word Kalos, meaning beauty).
Nora (from Eleanor - another 4-letter name)
Mara (from Mary - Let it Be)
Sadie
I loved the suggestion to kick Ella up a bit to Elsa or Elza! Ella is very popular, but also very pretty so I don’t dislike it!
I just saw your last post about using just Penny. I think it’s fine, and a very sweet name - your little lucky Penny.