Seeking YA novel from 90s(?) haunted/paranormal

[eulalia_vox]

Ok. I need help identifying a book. I'm like 73% (and declining) sure this is a real book and not something I just dreamed up.

Here's what I remember. My google-fu has failed.

I'm pretty sure I read it in the 90s. Young adult/teen. No idea author/publisher/cover/title.

The protagonist is a 16ish year old girl. Her parents are artists. I think her mom is a chidren's book illustrator. Dad gave up art & became a farmer. They may be separated/divorced. Definitely some strife.

Girl & dad move, i think, to his family home. It's a big old Gothic-type house. Weird, supernatural goings-on. Family's a little kooky.

Girl makes friend in school. Boy lives kitty-corner. Boy is cute but has big ears?

Maybe Canada?

Maybe seances, maybe mirror. Definitely evil family ancestor, Scottish, I reckon. Definitely remember them calling bad guy ancestor "laird." Laird Greagor?

Girl is only one who can defeat him. I remember the family and girl and boy have a plan and a final seance. Maybe a black cloak, swirling evil spirits trying to break chain of hands.

Girl prevails, happy ending.

Please, please, please somebody recognize this book with this crazy description. It is driving me up the wallllllllll.