Meredith sits down with her sister, Brette, to tackle two family-themed letters from the Love Letters column. First, a woman feels some tension with her future sister-in-law. Second, a writer discovers that her boyfriend and her mother had a one-night-stand in the past. Should the woman confront her mom? Does the mom even remember this guy? How are they going to make it through the holidays? Send your own letter to loveletters@boston.com.