The simplest thing would be to ask the third wife. Presumably the daughters are not on good terms with her so haven't wanted to do that, but it's a perfectly reasonable question.
I am not a lawyer but when someone dies if there is a will there will be an executor, i.e. nominated person who sorts everything out. The executor will eventually have to get probate, i.e. legal permission to distribute the assets, and from that point on you can pay to see the will for a small fee. Probate is often granted quickly if the estate is simple.
If the executor hasn't yet got probate I don't think there is any official way you can find out.
If there is no will, someone has to step up and volunteer to be the administrator, which is the equivalent to an executor named in a will. The administrator also has to get probate.
As for the third wife getting everything, it depends on what the father left. If the house was in joint names with the third wife, yes, she will get that. If he also left a lot of cash, savings, investments and so on, the wife will get a large chunk of that but the children might be entitled to some of the rest. It depends where in the UK they live (different in Scotland, I believe). Life assurance would get paid to whoever the deceased nominated as the beneficiaries. Pensions ditto, if there is anything to pay out (death in service benefits, for example).