Quite frankly, just reading your letter and all its various dilemnas I am shell shocked, and probably not even able to think straight.
You certainly have a host of semi related problems on your hands, and of course now with both a third child almost due whilst you yourself have your own mental issues, the whole scenario is truly mind boggling.
However, as far as I can see it, this is not your fault as you seem to have not only conquered your mental issues despite no family help,plus you seem to be taking a sensible view of your life with three children to rear over the next considerable time.
Two miles distance is absolutely no distance at all,whilst if this house is not only your preference, but will cater well for your entire family,I cannot see why all this aggro ..............other than from a seriously demanding mother.... whom sadly thinks just of herself and is not ready to see and understand your needs and point of view.
It seems to me, you really have to put your own family`s needs first, and I wish you luck in obtaining this new home soon.
Whilst perhaps once the deed is done your mother will realise that she is very much in the wrong, and she will,in time,come around to seeing common sense and that this home is indeed well within her visiting distance ...........if only she makes the effort.
Altogether a very upsetting story and I can but wish you well from all aspects, and I hope this whole business eventually works out and proves you right.