Sonia I've read House of the Spirits and watched the movie as well (with Antonio Banderas, Winona Ryder) and there's nothing to do with Daughter of Fortune. They are not part of the same story. Portrait in Sepia is indeed a sequel, which follows the story of Eliza Sommer's granddaughter. It's not even directly connected to Daughter of Fortune, so you don't need to read it first.
Erin House of the Spirits was written first, but is the third book if you read them chronologically. This is the first; the characters in The House of the Spirits are mentioned very briefly at the end of the second book (Portrait in Sepia). The earlier books chronologically are more like 'prequels' - none of the characters in them are mentioned in The House of the Spirits, as it was written years earlier.
Penny Lane No, not at all. The three books are a whole story in itselves; if you read the three you'll find common characters here and there. Anyway, Daugther of fortune is the first, if you read them in chronological order.
Judy I'm almost finished with it, and there's no hint that it's part of a trilogy. Fully self-contained as far as I can tell. (also I'm enjoying it very much)
Sarah They are vaguely connected - Portrait in Sepia follows Paulina del Valle's granddaughter and The House of the Spirits also features descendants of the del Valle family.