Oh V.
That is something that my son's father wld attempt. I know right now he is up to something but don't know what, so I have a bit of a feeling as to what yr sis is going through.
I feel sure she will get him back - fathers like that do it because they haven't and refuse to move on and have that bitter streak in them. They also, very falsely, think that in their very warped way, they will look 'good'. They need impact to make them 'get noticed' as the attention has been off them for so long - he sounds like he is in the gutter, with having done what he has done.
It will catch up with him - well, you will know that anyway, as you are in the force, so although the time between now and when he gets back to his mum, will be anxious and tiring, she will get him back.
My thoughts are with you all V.
Take care.