To be honest, it is neither of that.
His family members are obviously oblivious to these things. His sons have (apparently) no issues with their secret sister and Jemima has had numerous relationships as well.
They are British and it is not a problem for them. If Imran's family was conventional in Pakistani terms, it would have created problems for him, so it is good that they are not.
However, is it acceptable in our society? You and I both know that it is not. You are obviously not ignorant to the social and ethical issues in Pakistan (unlike the overseas Pakistanis) because you were born and brought up here, and you also know why it is a "big deal".
It is not going to have any influence on people who do not know Imran personally. Generally, the actions of your family and the people around you have more impact on you than what a public figure does. Nonetheless, people are going to talk about it and the political rivals will use it as a tool to attack him with.
Obviously they have skeletons in their closet, but politics and hypocrisy go hand-in-hand, something Imran himself is fully and wholly aware of.