The downside of sequels

I've started reading Guy Gavriel Kay's Ysabel, which I knew was a sequel of sorts to the Fionavar Tapestry trilogy. Which I haven't read for fifteen or more years. Forty pages in, I just hit characters that I know are from the trilogy, but heck if I can remember anything more about it/them than that. So I'm dilemma'ing: to continue reading, or to stop until I can reread the trilogy again...?

Probably I'm going to keep reading, while I have inlaws to play with the baby, and put the trilogy on my reread list. I have them at home; surely I'll eventually find time there to reread them...?