My oldest daughter is Emelia Greer, nn Emmie.
Which do you prefer for her sister…
Madeline Ruth or Ruth Madeline?
I like the LINE pronunciation and am considering Madeleine as the spelling, just not sure yet!
Edit to add… I’m also considering Ruth Eloise.
I like both names but prefer [name_f]Madeline[/name_f] (this spelling for the “line pronunciation), especially with older sister [name_f]Emelia[/name_f]. I think Emelia’s sister should also have a longer, frillier name to avoid one sister feeling that the other got the better name. Congratulations! 
MB
I personally prefer [name_f]Madeline[/name_f] as a first. And I think if you want the -line pronunciation then [name_f]Madeline[/name_f] is the most intuitive spelling. I could see [name_f]Madeleine[/name_f] getting mad-uh-lane or mad-uh-leen sometimes.
i love madeline ruth! if you want the -line, pronunciation, definitely go with madeline since most people would pronounce madeleine with a -lyn or -len ending.
It may depend where you live but I swear where I live both these names become -lyn so if you don’t like that I wouldn’t use Madeline/Madeleine as a first and keep it in the middle spot. [name_u]Or[/name_u] just try to check that it won’t be a struggle to get your preferred pronunciation.
I love both [name_f]Ruth[/name_f] [name_f]Madeline[/name_f] and [name_f]Ruth[/name_f] [name_f]Eloise[/name_f]!
[name_f]Madeline[/name_f] Ruth!!
[name_f]Ruth[/name_f] [name_f]Eloise[/name_f] and [name_f]Ruth[/name_f] [name_f]Madeline[/name_f] are both so perfect!!
However, with older sister’s name I like [name_f]Madeline[/name_f] [name_f]Ruth[/name_f] best 
Regardless, all of your options are incredible!
I think [name_f]Madeleine[/name_f] [name_f]Ruth[/name_f] would be lovely with your daughter’s name! I specifically like the [name_f]Madeleine[/name_f] spelling because I think it matches better with the slightly-out-of-the-ordinary spelling of [name_f]Emelia[/name_f].
[name_f]Madeline[/name_f] [name_f]Ruth[/name_f] with sister. Definitey use [name_f]Madeline[/name_f] spelling for the pronunciation you want (lovely!) [name_f]Madeleine[/name_f] is not pronounced that way.
I also think [name_f]Ruth[/name_f] [name_f]Madeline[/name_f] and [name_f]Ruth[/name_f] [name_f]Eloise[/name_f] are lovely and also work fine for Emelia’s sister, so go with [name_f]Ruth[/name_f] if it is your favourite.