Dear Lazza
Things seem to have become very over-heated here and the main thing is not to react in a way which might increase the tension.
So leave aside any dispute for the moment about whether your children will or will not have contact with grandparents. At this stage, your W needs support, not an argument. If she disapproves of contact, that wish is to be complied with until it can be discussed in a more positive atmosphere. My guess is that this is an issue of control, and it just happens to have focussed on the grandparents.
With regard to the post-natal depression; the best person to speak to would be the doctor. The doctor cannot comment on your W because of patient confidentiality, but they can listen. If your doctor thinks your W cannot cope, they will decide what to do about that. But please note; PND does not mean incapable; if you are the sole wage earner, that presumably means that your W is coping with four children while you are at work.
You have mentioned the house has 5 bedrooms. Would it be possible to put a pair of the children togther and temporarily move yourself in to one of the rooms? Not ideal, but it may get enough heat out of the situation to let everyone calm down. Explain to your W that it isn't practical for you simply to move out since that would mean switching money away from the house and family in to expensive short-term accommodation. This is not in her interests.
Fairly quickly, take legal advice on the procedure that your W would have to follow if she wishes to get a court order. Your W is fully entitled to research this on her own behalf and either of you can visit the Citizens' Advice Bureau as the first office of enquiry.
http://www.adviceguide.org.uk/index/...ent/family.htm
You need to speak to a lawyer about whether a court order could be made as the general advice only covers areas such as abuse. If you do move in to a separate room, put in writing that you are doing so only as a way of co-operating in a difficult atmosphere and that you don't wish it to be misunderstood as a separation. (This is just a technical point, but it does need to be covered as it is possible to be separated but living in the same property.)
Right at the moment, though, the most important thing is to resist any inclination to argue no matter how justified you may be. If you argue, this will be like chucking petrol on a fire. It won't put the trouble out and it will make things worse. It must be very hurtful to have your W in dispute with your parents, but if push comes to shove, your W has to know that you will take her side, even if you happen to disagree with her.
If your W has coped with child number 4 and moving house in the past year, then she has my sympathy and admiration. Remember that it is generally acknowledged that moving house is only marginally less stressful than coping with a death. No matter how good the housing, the actually process of moving is inherently upsetting.
I hope things begin to calm down in a few days and then it may be possible for you and your w to get some help with communicating again.