OWW
I suspected as much re harassment order. 
I would notify police that he has been attempting to circumnavigate contact, that you are concerned about your safety and safety of your children. I know this might seem a little knee jerk, but is a sensible precaution in my book.
Part of me gets all 'I don't see why you should feel intimidated or alter your every day activities' because FX is a nasty, nasty man... But at the same time I think there's something to be said for your mum being wary of being followed if she comes to yours and you being cautious if you are out and about and returning home.
I don't mean to make light of your situation, but i now have a fabulous mental image of your mum checking her rear view mirror to see FX following her and executing a gene hunt style handbrake turn as FX plummets to his doom off of a poorly signposted dock-side
Dumbledore likes Derren Brown. 