Middle names aren't all that important. They are useful for distinguishing YOUR Adeline from others in official documents and so when you are really angry you can say "Adeline Jane, get down here this MINUTE!"
Other than that .. they don't really have to 'flow' or 'sound right.' Commonly middle names are family names, where you might want to honor and memorialize a relative, but don't want to use it as a first name. Or just another name you like. For my daughter, who has a somewhat uncommon first name, I chose Elizabeth -- on the logic that if she didn't like her first name as she got older, she could use any of a dozen versions of her middle name instead.