Pathological liar

Applegran
you said you remember "reading that the brains of compulsive liars are different from the rest of ours" You may have seen something about the brain imaging studies research.
There are studies, forgive me for not spending time looking them all up. Some include studies on Psychopathy/Antisocial Behaviour Disorder which has as a diagnostic criteria "compulsive lying". The studies found more white matter than gray matter in the prefrontal cortex* of the compulsive liars.
* the area of the brain that enables people to make moral evaluations and feel guilty about doing wrong.

In the case we are talking about here, we don't know if there is is a pathological reason. However drivergran would have been regarded as a very good relative for giving actual the examples of behaviour she gives here if she had spoken to us when I was involved in research at the Institute of Psychiatry! Many people have disorders or are on the end of the spectrum of a disorder which, by its nature, does not mean the person themselves comes for advice/help. Often it is relatives who have to ask for help and then we need to ask for as much info as they could give us.
However, as I was about to say, we can't tell what is actually going on here in terms of clinical explanations. I think the best thing we can do is support the OP and her daughter with suggestions as to what we might do or maybe some people have some experience of this and can tell us how they coped.
There are quite a lot of conditions in which compulsive lying is a feature. So I would advise her daughter to go to the GP and talk it over if she needs help, and be ready to describe other behaviour and personality traits her husband has. I do hope the poor girl's life begins to improve once she addresses this issue. I really can't see how she can manage her life trying to live with it, unless he never does it at home!

I think there is a difference between those who exaggerate, such as men down the pub saying they earn more than they do, and pathological liars who can be con merchants and cause serious problems to those around them.
I know someone who tells quite serious lies and he does believe them when he repeats them. He also believes that everyone lies.

GoldenAge Please don't take this the wrong way, I'm only wondering, not arguing,- you mentioned someone you said was slightly autistic who, from what you've said gives different stories to different people. I just wanted to say in passing that if he is actually Autistic he isn't likely to be deliberately lying. One of the things about Autism is that people are very literal in what they say. He may not interpret what he sees accurately though because if there is a social exchange involved, especially if it is a bit subtle, then it would go over his head, if he's autistic. I did research on Autism. One reason I love Autistic people is because they just can't lie. Maybe this lad you know seems autistic but has a different kind of developmental disability.
Hope you don't mind me mentioning it! I'm slightly on the fringe of the Autistic spectrum myself so I tend to be a bit pedantic, but there's absolutely no bad feelings involved. Like my cousin who is the same, we love discussing things! Thanks.

GrandmaMoira I think you make really good point in so clearly showing the difference between the person who likes to exaggerate a bit for effect and the con-merchant. Apparently some people lie and do believe their lies! I have not met anyone like this though. I think too your point about the liar believing everyone lies is very important. It made me realise that they live in a different world where they think everyone has low morals regarding telling the truth. How depressing. I find it very hard to deal with liars. I grew up with a half-sister older than I who was one of those who lied in preference to the truth and even lied when it was of no purpose to her. I used to get so distressed and confused as I stood by her side when she was telling these awful stories. I simply could not abide it, it was as if someone was filling my head with pebbles! When I asked her why she did it she used to get so angry with me and threaten me with terrible things so I learned from very young to keep quiet. I honestly think my migraines started because I used to have to be brought home from school by her and she used to lie all the way to the other children until we arrived home. Every day by the time we were back home I had a terrible head ache!