Hi, this is super late but I was reminded of it and did a google search.

Liz is my dad's sister (though I've not been on contact with my dad's family for 25 years).

I'm under the impression the "Mistress" version of events is the right one.

My mum told me that even when Liz and Brian were together, Brian still lived with his wife and didn't want to break up their family life, to protect the kids. Maureen is said wife. I'm unsure if they ever did divorce/Brian and Liz ever married, but I suspect that lots of people assume he and Liz were married which is why you see obituaries mentioning His wife Liz and their two sons (even though the sons are not Liz's children).

Then it looks like in some cases people have read and "fact checked" obituaries because very similar wordings come out with "his wife Maureen, and their two sons"