Changeling: The Lost and Geist: The Sin-Eaters

[magic-rhyme]

Changeling: The Lost and Geist: The Sin-Eaters seem very similar in some ways.

I'm looking for suggestions about either a cross-over between the two or perhaps a hybridization of the two.

Any suggestions or tales of experience to share about combining them or cross-overs between them?

[Prince of Cincinnati]

well it would be easier if say a Darkling with Contracts of Shades and Spirits to work with a Krewe. Or how about a single Sin -Eater just discovering the fae.
Or a old haunted house is up for sale and the buyers are the changelings and sin eaters.