They are a little similar for my taste – not only do they share similar sounds, but they even mean basically the same thing. They do have different origins, though, so I suppose that helps. [name_f]My[/name_f] biggest consideration would be if you are planning to have future children and how similar they might sound in a sibset with other distinctly different names.
But, honestly, if you don’t love any name more than [name_f]Adeline[/name_f], you should should use it! They’re not so similar that it would stand out, like, say, [name_f]Audrey[/name_f] & [name_u]Aubrey[/name_u].
Still, if you are open to other options, I might suggest these:
Overall, though, I do think [name_f]Audrey[/name_f] & [name_f]Adeline[/name_f] would be fine as sister names.