hugely important, if any survivors are left and able to make an accusation against the house that wiped out their family, the ruling houses then brind down Drow 'Justice' which is when the students of the academies are brought together, often along with Drow of the ruling houeses and make a public display of destroying the 'Murdering' house.
Essentially it works thus:
House A is weak for whatever reason, in this case we shall assume because they have lost favour of Lolth
House B is a lower ranking house in the cities heirachy, but feels they are able to decimate the weakened stronger house therefore ensuring they gain in power themselves.
one of three things then happen:
House A Manages to fend off House B, in which case those that are left will make accusation against house B to the ruling houses, and the drow 'justice' mentioned above ensues.
Note: House A Does not regain Favour, and are likely in even more danger unless they can right whatever wrong they commited
House B Slaughters Every Noble member of House A, with the exception often being commoners, House B strangely grows in size overnight, coincidently by the same number of commoners not killed at House A. And the Ruling houses (and all the rest of the city) secretly applaud House B for their Cunning.
House B Believe they slaughtered all nobles, but infact did not, one or two Nobles remain alive, they make accusation and House B meets Drowish 'Justice' Usually those surviving Nobles (and often common soldiers that chose to abandon House B) will either be given to one of the ruling houses or be auctioned off.
Essentially, Lolths Displeasure covers the entire Noble family, with only a small number of ways to regain it generally.
Is it only a matron mother's mistakes that can be counted grave enough for the entire house to lose favour, or is it enough that one member of the family for example turns to Eilistraee?
Any member of the family (including the commoners) can bring the disfavour of lolth upon a drow house.
However, I do not believe say... a commoner turning to eilistraee causes disfavour on the house as a whole usually, though it might if it was one of the nobles that did. Usually it takes direct insult toward lolth or her following to cause such a thing (Drizzt had to spare a wood elven child for example to cause disfavour upon his house, and More than a few characters in the War of the Spider Queen Series are far from devout followers but seem to have little effect on their houses)
Good Reading material for Drow:
R.A.Salvatores Drizzt Series, especially the early ones, no matter what anyone says, he essentially created the Drow Society that we all know, regardless of peoples distaste for Drizzt.
The War of the Spider Queen Series (again Salvatore has a hand in them, but they're awesome for giving detail on drow)
The 3.5 Underdark Book.