こうかな?

class A:
hage="hage"

class NewClass:
hoge=A()

a=NewClass()
b=NewClass()

b.hoge.hage="huga"

print(a.hoge.hage)
print(b.hoge.hage)

class NewClass2:
def __init__(self):
self.hoge=A()

a=NewClass2()
b=NewClass2()

b.hoge.hage="huga"

print(a.hoge.hage)
print(b.hoge.hage)