He has been incredibly nice to her and now she is starry to doubt her decision.
Sorry OP. This is classic manipulation. See also - the unfaithful husband, who is "so sorry & devastated" ... he's not sorry about the affair - he's sorry he's been found out.
He's being "nice" because he's desperate. Not because he's nice.
Nice men don't scream in their wife's face, or lie to & steal from them.
Funny how he didn't take himself to Gamcare until the shit hit the fan & HE was faced with a consequence of his actions, huh?
He didn't think to contact them when only DD was suffering the consequences.
This is an entirely self-serving gesture.
He has told her it’s no problem if she lives in the house to work her notice and he will treat her with respect.
Respect? What a woolly concept. Even he he had defined what he means by it - why should DD believe a liar?
DD should be very wary. He wants her back at the house so he knows where she is - & if necessary (ie she doesn't instantly agree concessions, extra chances, a date to 'forgive him' by ...) & will be able to control her.
How do I know this? - Because THIS:
His parents are now starting to get nasty phoning her hip and telling her she should stand by him and help him.
The abusive apple didn't fall far from the tree did it?
She is not obliged to take their calls.
She does not need to be guilted into any Stand By Your Man bullshit.
Have a read of this OP - your DD is being manipulated back into the FOG of a dysfunctional marriage, to a man from a disordered family. It is fucking outrageous that his parents are ringing her up to bully her. She should block their numbers immediately.
outofthefog.website/toolbox-1/2015/11/17/fog-fear-obligation-guilt
Above all, you need to reassure your daughter -
SHE IS NOT RESPONSIBLE FOR HER HUSBAND'S ADDICTION.
&
SHE IS NOT A CYPHER FOR HER IN-LAWS DESIRE TO PRETEND THEIR SON DOES NOT HAVE HUGE PROBLEMS.