Dominus et Domina Dursley, qui vivebant in aedibus Gestationis Ligustrorum numero quattuor signatis, non sine superbia dicebant se ratione ordinaria vivendi uti neque se paenitere illius rationis.
The Master and the Mistress Dursley, who were living in the house designated by number four of the Drive of Privets (signatis numero quattuor Gestationis Ligustrorum), not without pride said that they conducted their life in an ordinary style and did not regret that style.
The first half of this is simple enough. Dominus and domina mean the male and female heads of a household. They can also be used for lord and lady, and Dominus is commonly used for God in Christian Latin. Needham chooses these as a good Roman equivalent of Mr and Mrs.
Numerus clearly means number. In aedibus means in a house or in the house. The connection to edifice should make it easy to remember.
Paenitere, to regret, is the ultimate source of English words like penance and penitentiary.