I think they work. The thing to remember is that siblings are only with each other 24/7 for the first decade or so of their lives. They don’t have to be perfectly paired to be good names.
Personally? I think you should spell Madeline properly so that it doesn’t get dated quickly. The switching vowels for Y is very trendy but won’t be for long. It also comes off as unintelligent. Read the post at the top of this board, it really explains why names shouldn’t be tinkered with.
Re: Madelyn and Magnolia