Harping my own story. Although it is much more than a claim fic, The Unexpected Universe does have Spike claim Buffy and make her part of the clan.
The Unexpected UniverseSummary: This series of stories picks up at the end of Season 2, The Becoming 2 and goes off canon about half way through that show. You'll find familiar challenges for Buffy and the Scoobies with UNEXPECTED results as Spike faces them with her. If you like a story with love, romance, sex, fights, angst, tears, laughter, marriage and babies then you're in the right place! I hope you enjoy it!