Parenting advice for friend

[Lilyargin]

A friend, recently separated from her partner, is having a tough time with her children, 8 & 3. The older one constantly winds up the younger one, to provoke conflict, tells terrible lies to my friend to get attention/worry her and plays her off against her ex.
My friend ignores lots of bad behaviour and then suddenly explodes, saying really upsetting things to the oldest child.
There are very few boundaries, almost no consistency - sanctions are threatened but never carried out - and the eldest child says awful things to my friend.
I know that giving parenting advice can be very inflammatory, but I don't want to ignore her struggles and I have seen the situation getting worse over the years.
I feel it would be remiss not to try to help and want to suggest some things that my friend might try, or recommend a book, but I'm not sure how to approach the matter.
Interested in ways to approach this/being told to stay out of it.

I don't think you can say anything. It will always come across badly.

My favourite, honestly I have nothing to do with representing them. I just found programme amazing as a parent

The incredible years programme.

I did it free delivered by a local charity but you can buy the book or rent from library or audiobook.

https://www.amazon.co.uk/Incredible-Years-Trouble-Shooting-Children/dp/0578434512

A quick way to lose your mate.

Don't say anything

The trouble with not pulling up mates/siblings/friends/parents about anything is that bad behaviours will then prevail.

I really think that we , as a society, should be able to call out bad behaviours. It might help to prevent some needless deaths/suffering.

We really are a put up and shut up society.

Has she actually asked for advice?

Don't intervene- unless you are 100% sure it's abusive.

Totally agree...Still seems to be a British tendancy to 'keep out of others business for fear of seeming rude' even where the welfare of children is concerned sometimes, which is dangerous for them if abuse and neglect are a factor

Thanks for the replies. She has I been open to advice in the past and admits she is despairing of the situation so I think she would be receptive to suggestions.
@SpamFrittersYouSay I really agree. I feel it's my duty to help, as I can see this getting worse, and I fear that as the children age and become teenagers, these patterns will have become entrenched.
The child who often instigates trouble has a sense of unfairness, of always being blamed and this is damaging too.
I think I'll recommend a book rather than saying 'I think you should do this'. I'm not an expert, but am older than my friend.
Thanks for the book recommendation @Hankunamatata