以下是一个示例代码来实现题目要求的功能：

students = []

class Student:
    def __init__(self, name, score1, score2, score3):
        self.name = name
        self.scores = [score1, score2, score3]
        self.average = sum(self.scores) / len(self.scores)
    
    def get_grade(self):
        if self.average >= 90:
            return "A"
        elif self.average >= 80:
            return "B"
        elif self.average >= 70:
            return "C"
        elif self.average >= 60:
            return "D"
        else:
            return "F"

# 添加学生信息
student1 = Student("Alice", 85, 92, 78)
student2 = Student("Bob", 90, 88, 94)
student3 = Student("Charlie", 76, 85, 92)
students.append(student1)
students.append(student2)
students.append(student3)

# 按照平均分降序排序
students.sort(key=lambda x: x.average, reverse=True)

# 打印学生数据
for student in students:
    print("姓名:", student.name)
    print("平均分:", student.average)
    print("等级:", student.get_grade())
    print()

输出结果为：

姓名: Bob
平均分: 90.66666666666667
等级: A

姓名: Alice
平均分: 85.0
等级: B

姓名: Charlie
平均分: 84.33333333333333
等级: B