In a medium bowl, toss peaches with granulated sugar, lemon juice, ½ vanilla bean seeds, and vanilla extract. Let sit for 30 minutes at room temperature, stirring occasionally. Strain juice mixture into a small bowl, and set aside.
In the bowl of a stand mixer fitted with the whisk attachment, beat cream at medium speed until thickened. Slowly add confectioners’ sugar, and beat at medium-high speed until stiff peaks form. Add mascarpone cheese, and beat at low speed until just combined. (Do not overbeat.)
In 6 (12-ounce) glass cups, layer 2 tablespoons crushed honey graham crackers, ¼ cup whipped cream, 1 tablespoon lemon curd, and about 3 peach slices. Repeat layers once. Place remaining whipped cream in a piping bag fitted with an open star tip (Wilton 1M), and pipe on top of peaches. Serve with reserved peach syrup. Garnish with basil and graham cracker crumbs, if desired.