HELP! Where do we stand?

[Asteria]

DH is having massive issues with his ex.
As briefly as possible: he has made enormous sacrifices in order to maintain regular contact with his children, to the extent of moving house three times and driving hundreds of miles each contact weekend. She sold the marital home (she changed the locks and took the entire contents - including his personal items - and about 85% of the equity, plus DH took out a loan to keep her going financially in the interim) and moved 250 miles away with no discussion about location (she led him to believe it was considerably closer and then claimed to have thought long and hard about the more distant location she went with - implying that she had been trying to hide her decisions from DH), schools or consideration of contact between the children and their father (he was told to "deal with it"). He eventually moved closer, but still a couple of hours drive away as he could not afford to leave his job and did not want to impact on his maintenance payments.

DH, my DS and I recently made considerable sacrifices to move to within 30 miles of her (DS and I were living at the other end of the country before the move), so as to ensure DH and his children would spend as little time as possible in the car during contact weekends. DH collected the children on fridays and his ex collected them from us on sundays. Despite being very open about our planned move for months beforehand, DH's ex then announced that she was moving within 3 months of us moving in, to over double the distance away from our new home.

The initial agreement, after her move further away, was for her to drop the children with us for contact weekends and for us to return them so the 50% split on travel continued for the best part of a year in total. She has now refused to do any of the travel, stating that she would withhold access to the children if he refused to take on 100% of the travel - her partner has just called and confirmed that they are now withholding access unless DH complies to their demands. Her grounds for not doing 50% are for financial reasons, however her partner has just offered DH £100 a month as compensation for him doing all the travel - leading us to the conclusion that she simply cannot be bothered rather than there being any financial implication involved on her part.

There are many other silly little issues involved in this, like her refusing to send the children with clothes or footwear and withholding access last Christmas. Essentially she is using the children as a weapon against DH. I am of the personal opinion, having spent a considerable time trying to negotiate with her on all manner of petty little issues that she has had, that she is mentally unstable - narcissistic at the very least. There is a strong history of it in her family.

Our primary concern is for the children, however DH has been under considerable stress for many years at the hand of this woman to the point that it has had a severe impact on his health.

We want to take it to court but can ill afford the costs that this will incur. What advice do you good mumsnetters have about self-representation in such cases?
Many thanks

If she hasn't moved yet he could apply for a prohibited steps order. The court has the power to prevent a change of residence for a child.

Such orders aren't lightly made however. If the mother has a genuine reason for the move (and it seems she does not) courts are loathe to interfere.

How old are the children? Could they live with you? Moving them from one end of the country to the other can be very damaging if the only reason for the move is to frustrate the other parent.

She has moved them twice now, both mid-school year (the more recent move was mid-term) and both within a year of each other to pursue relationships she is/was in. We looked into prohibitive steps before the last move, however my DH was worried that she would withhold access to the children. Now she is withholding access so he has nothing to lose. He spoke to the NSPCC earlier and they have backed him up on everything saying pretty much every step she has taken over the last 2 years has been illegal and immoral.
Our worry is that she is totally unconcerned by how her behaviour could impact on the DCs and there is every chance that she will up her bad-mouthing of their father (she already tells them that he is fat and lazy etc) and upset them more. They are 5 and 7 so we want to tread as carefully as possible to minimise any long term damage.
We would happily have them living with us and have looked into schools for them here, our worry would be how she behaved towards them during access time with her and moving their schools again - they are in their 5th school already. The last thing we would want to do is traumatise them any further.