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It does seem a coincidence that they all died in November, but this coincidence has been made into something of a joke.
In the first place the reverend gentleman himself died on November 1st which is the feast of All Saints. This was felt worth noting on the tomb, perhaps in part because All Saints Day is the festival of the Christian dead. There was no need to mention that All Saints Day is November 1st as everyone knows this (or might be assumed to).
The 8th day of a feast (i.e. the same day of the week as the feast) is generally known as the "octave". If someone died on November 8th normally it would be very unlikely to be noted as the octave. However, when the daughter died on November 8th and the time came to add her to the inscription, the coincidence was felt worth noting. The father on the day of the feast and the daughter on the octave of the feast. Again, since "octave" is a recognised word for the day exactly one week after a feast, everyone would understand what was meant.
Lastly, the wife died on November 14th, and the person responsible for her inscription had something of a sense of humour. Although the octave of a feast is a recognised concept, there is not really any such thing as the fourteenth day after a feast. Since the death of her husband and daughter were both inscribed in relation to All Saints Day the person responsible thought to do the same. But nobody would ever really refer to November 14th as the Quartodecimo of All Saints, and so the actual date November 14th was also mentioned.
It is a little like saying X died on Christmas Day, Y died on Twelfth Night and Z died on Fifteenth Night. Twelfth Night is a "real" thing, Fifteenth Night is merely jocular.