Pour 3/4 cup boiling water into a small bowl. Add lemon gelatin mix; stir until dissolved. Pour 1 cup vodka into a glass measuring cup; add enough ice to make 1 1/4 cup. Stir into lemon gelatin until slightly thickened; remove any unmelted ice. Fill tall shot glasses 1/3 of the way with lemon gelatin mixture. Refrigerate until lemon gelatin layer is set, at least 90 minutes. Pour remaining 3/4 cup boiling water into the small bowl. Add orange gelatin mix; stir until dissolved. Pour remaining 1 cup vodka into a glass measuring cup; add enough ice to make 1 1/4 cup. Stir into orange gelatin until slightly thickened; remove any unmelted ice. Pour over lemon gelatin layer. Refrigerate until orange gelatin layer is set, at least 90 minutes. Pour 2 tablespoons warm water into a bowl. Add unflavored gelatin; stir until dissolved. Stir in condensed milk and rum. Pour over orange gelatin layer. Refrigerate until top layer is set, at least 30 minutes.