Bob
First of all, I am really sorry to hear about the situation you are in; it must be awful. It is difficult to know what to suggest that is helpful.
It does seem to me that you need to sort out the finances so that you both have some degree of certainty about who is going to have to pay for what and so on.
Is there any chance that the two of you can come to a financial agreement between yourselves and without the full involvement of lawyers? If you can't manage it by yourselves, you could try
mediation. If you don't know about mediation, there is now an article on the subject in the Wikivorce Library.
One or two things do strike me - first of all, as your youngest is living with you and the others are away from home, your wife doesn't have much excuse for working only 15 hours. You want to ensure that everybody important is thoroughly aware of this - and the fact that you are working excessive hours to provide for everybody. This should have a bearing on any spouse maintenance.
Secondly, if the house has negative equity, it reduces the 'family pot' and may be set off against some of the value in your pension. This means that, although you wife may get a portion of it (even if she doesn't deserve it), it should be less than she would have got otherwise.
As far as the house is concerned and assuming you retain it after the division of assets has been completed, could you trade down at some stage to something smaller and use some of the released cash to pay off part of the mortgage? This would reduce your monthly expenses. (Unfortunately, when you change houses, the government will want a slice in the iniquitous stamp duty, which doesn't help.)
On the other hand, house prices will recover at some stage and, if you can struggle on, you might do better to retain it - who knows?
Not very helpful I'm afraid, but this is the best I can do without knowing an awful lot more about your whole situation.
I hope things work out as well as possible for you.