There are as many problems with houses as there are with signs. The key, and obvious one is that there is no agreed method of calculation - all use 30 degree arcs for each house, which in a real sense makes all houses equal. The problems are that there's no agreed definition of 'arc' here, whether it's time or space are two obvious differences. Also 'equal' at what 'place'? Houses are two dimensional representations of 3 dimensional space and latitude affects the 'projection' of house cusps.
I'm one of those who is fairly blase about the 'mess' of house definitions, I tend to use either Regiomontanus or Placidus, not because I believe these have any mathematical superiority but because I like them LOL.
Do planets rule houses? Accidentally yes they do. But it is only 'accidentally' that is related to the specific chart you are looking at. Saturn may 'rule' my Seventh,as I have Aquarius on the descendant, but that does not mean that Saturn has any particular essential links to partnership, matrimony, etc. It's a significator of those in my chart but we need to distinguish between signification and essential nature. So 'ruler' here is a shortened form of 'ruler of the sign on the Seventh cusp'.
Astrology also has built up a whole series of natural correspondences. Now there have been many attempts to try and reform or clear these out. Trouble is they are still with us and are so imbued into the subject that I think that's something of a losing battle. But again there's a need to distinguish between the 'sympathetic' side and the essential side. Cancer may naturally be associated with the fourth house but that's a very general association and we shouldn't run away with the view that a specific fourth house is 'Cancerian' in nature. So in a sense the Moon has some links with the fourth but those links are at a very general level and unless your fourth actually is Cancer then it's best to forget about them.
Dave neatly sidestepped the question about where he would look to describe the Mother, (or for information and issues relating to the Mother). Now Dave's list of lunar associations is psychological, that doesn't invalidate it at all but it is not comprehensive. I'd certainly look at the condition of the Moon when trying to describe the Mother. The Moon is the premier female significator in any chart, be that wife, mother, girl friend (there are those who would go so far as to say that the Moon is the prime significator of a chart full stop).
So the Moon needs to be considered for the Mother. Dave points out that the fourth relates to the parents (among other things) and if we need to separate the parents and consider one, tradition has the father taking the fourth and the mother taking the tenth (as the father's partner). So I'd also look at the ruler of the tenth (in the above sense), even if this were Saturn. Indeed some psychologists might have a field day with that one, with mothers trying to play the role of fathers and being principle breadwinners or carrying the social status of the family. I'd also look at planets in the tenth - If I were a disciple of Morin, I'd even say that planets in the tenth carried more weight than Lord 10, if he or she were an absentee landlord (i.e. not in the tenth).
My point on the above is to really stress that there is not just one significator of the mother, there may be two or three and all would need to be considered.
The more I read of Astrology the more I realise just how diverse it is and that there are a whole load of traditions and views. The idea that at some point Astrology lost it's direction and needs to be restored is also a fairly widespread one. Dave says as much with his comment on the Greeks. This suggests that there was a 'pure' form of Astrology, a sort of Astrological Garden of Eden, from which we have fallen into error. In the Renaissance the blame was attached to the Arabs, to the Hermetics, to the practice of Judicial Astrology, etc. The Astrologers that Dave mentioned also tried to reform it and put it back into working order. Ironically they too are now seen by some as the reason Astrology 'failed' and there is an attempt to restore 'Real Astrology'. I saw a comment the other day from Benadette Brady who said that in 10 years Traditional Astrology would have 'won'. It's a tongue in cheek comment but it shows that the reforms of one era can become the 'discredited' notions of another.
I n an analagous sense, Astrology is like Humpty Dumpty, it can't be put back together again but personally I think that is because it was never 'together' in the first place.