To make these pops without the liqueur, simply add an extra 2 tablespoons sugar.
Combine strawberries, watermelon chunks, lime juice, water, and sugar in blender. Blend 20 seconds, pressing down with wooden spoon as needed. Pour mixture through fine-mesh strainer, pressing with spatula, to remove seeds. Rinse blender, then pour strained liquid back into blender with liqueur. Blend another 20 seconds. Pour into molds and freeze 4 hours or overnight.