I like [name_f]Madelyn[/name_f] since I think that y looks so pretty in cursive and the pronunciation is really obvious, but [name_f]Madeleine[/name_f] is nice if you like a more [name_u]French[/name_u] vibe. Maybe try writing them in a fancy font or looking at the names on a stocking or things like that to get some inspiration. 
I am in [name_f]Canada[/name_f] and would pronounce it Mad-uh/a- line .
wow fascinating
Much prefer the [name_f]Madeleine[/name_f] spelling! [name_f]Madelyn[/name_f] looks a bit too trendy.
I like the [name_f]Madeleine[/name_f] spelling best and I think it goes well with [name_f]Emilia[/name_f]. However, if you are dead-set on having the -lyn pronunciation and not having to correct it ever, [name_f]Madelyn[/name_f] would be the most foolproof. That being said, I would pronounce [name_f]Madeleine[/name_f] as Mad-uh-lyn/len (those sounds are the same to me).
Madeleine is a perfect twin to [name_f]Emilia[/name_f]!
So, my only exposure to the name [name_f]Madeline[/name_f] is the kids book and if I recall the rhyming scheme of the first book correctly, her name did rhyme with line.
I think [name_f]Madelyn[/name_f] would get the pronunciation you want and is less confusing to spell. I don’t think it looks trendy. Like others have mentioned y is so pretty in cursive!
I’ve known three Madeleines who pronounced it just like [name_f]Madelyn[/name_f]! And I prefer [name_f]Madeleine[/name_f] visually, so that one gets my vote. I do think, though, that if you’re really worried about pronunciation issues [name_f]Madelyn[/name_f] would be simplest. Either works nicely with [name_f]Emilia[/name_f] as a twin set! I like that they’re completely distinct from each other but sound good together and share a similar vibe.