Leo and Chris didn't worry about Bella living in the luxury mansion area because Chris could live there too, he just didn't want to. And considering the difference in treatment that Instructor Hanna had between Leo and Chris during entrance exams, they knew that a good Awaken with a Quirk Special was far more valuable than a genius Awaken with a normal Quirk.
But despite being curious, Sophia didn't ask any more questions. She preferred to wait and see how they would handle it.
She could feel that Chris was just an Awaken Bronze 2 Stars, but it is known that in MU only young Bronze 3 Stars can be accepted, so for Chris to be able to enter being a Bronze 2 Stars there was another reason, both for the talent he showed, or maybe even for being the son of someone powerful.
As they didn't explain, she didn't try to find out more.