Husband's family

[Goldenset]

Could I please ask people's opinions on how likely it is for a husband's close family (mum, sisters, nephews, nieces) to know that he is having a longstanding affair but to not say anything to the wife? For context, we've been together over 30 years and I get on with his family. I wouldn't say I'm ultra close with them but I wouldn't say there have been any problems between me and them.
I don't have any proof about an affair. But something one of his family members said made me ask him.

What did the family member say?

She was telling a story to a couple of other relatives about some man she knows who had been unfaithful. She wasnt speaking directly to me but I was present. She has an exagerated style of telling a story and she can be quite funny so I was laughing - not at the facts of the story but at the way she was telling it. The others were speaking at the same time but I heard her say 'laughing coming from a woman whose husband has been shagging another woman for X years'. The X number immediately struck me as relevant to me.
I asked her later who she was talking about and she simply referred to the wife of the guy she'd been talking about.

I would ask outright it is is him she is referring to

Oh that doesn't sound good.

Had you ever had any suspicions about your husband before she said that?

Have you had any suspicions before that comment?

This was some time ago and there has been lots happened between then and now although he's never admitted to anything. But has shown what I now understand to be classic signs of being found out and then subsequently ending an affair.
I am left wondering whether some of them knew about it.

I had suspicions before, yes. I don't understand why she would have potentially dropped him in it though and he was present when she said it. I looked at him when she said it and he remained looking at her. Nobody looked awkward at all.

Well if this was me in this situation I would want to get to the bottom of it or it would fester away in my head and kill my relationship.
Ask the woman and also ask him

Doesn't sound like she knew. If he was there when she was telling the story and there was no awkwardness - then it may just be you imagining it.
I think the problem is more that you don't trust your DH.

Do his family have any issues with you? Do they like you and get along well?

I think you'd know if they all knew because they would dislike you and have a reason to keep a secret. If they get along well with you (and not just putting on a friendly face out of family duty) then the chances are it wasn't about you.