Using a small, sharp knife and following the natural curve of the fruit, peel the tangelos, grapefruits and oranges, removing all of the white pith. Cut the fruit crosswise 1/2 inch thick, then cut each slice in half; discard any seeds. [Make ahead: Transfer the prepared citrus to resealable plastic bags and refrigerate overnight.]
In a small saucepan, bring 1/3 cup water, the brown sugar and salt to a boil over medium-high heat. Remove the saucepan from the heat, add the lemon zest and fennel seeds, cover and let steep for 10 minutes. Pour the mixture through a fine strainer set over a small bowl, pressing on the solids to extract the liquid; discard the solids. Let the syrup cool to room temperature, then stir in the lemon juice. [Make ahead: Cover and refrigerate overnight.]
About 30 minutes before serving, pour off the liquid from the fruit (go ahead, have a sipits a treat for the cook!) and transfer the fruit to a large bowl. Gently stir in the sugar syrup and pomegranate seeds.
