What do you think of the name Adeline Faith and Declan James?
I love both names, though I do prefer the -line or -leen ending pronunciation of Adeline. Still, -lyn is a valid pronunciation, and I find your Adeline spelling the most appealing, regardless of how you prefer it said. No reason to change it! 
And for what it’s worth, it’s the nickname Addy (any spelling) that’s overly common at the moment. Not the given name Adeline, which is barely in the top 500! Especially considering Addison’s unprecedented leap in last year’s numbers (likely top ten this year). If it doesn’t concern you, all well and good, but even if it does, the simple solution is to just use a different, less common nickname. Ada, Adele, Dell, Della, Lynn, etc. No big deal.
As to the boy option, Declan James is a very handsome name, in full. Declan is slightly more common, at 364, but it actually SEEMS even less so, given the fact that it doesn’t happen to share a nickname with a more popular name and that boys in general are given common names far more often (making those that aren’t quite as popular come across as even less so, if you follow).
Both great choices, and I think you have nothing to worry about.