Christmas at the Whitman's house:
Mr. W: um, don't you think Finn's girlfriend is a little weird?
Finn's Sister (that was never named and will probably never play any part in the KK series or in Finn's life ever): YEah.
Mr. W: I swear I saw her pass the salt to Finn, but she never touched the salt.
Finn's Sister: Yeah, what the heck. . . you don't think she's. . .
Mr. W: oh my gosh my son is dating a witch.
And thus, Finn had to convince his family that Amanda is not a witch from that day untilthey were married and had kids. And when their kids had powers, they had to lie to the family as well.
Like this if you lie at Christmas time