"El ciento y la madre" = The hundred and the mother*

The world and its wife. Everyone and their mother. Near synonyms and synonym expression, Cool, huh? Yet, we Spaniards can go much further than that and include the grandmother in the picture by using this quite common expression too: "Éramos pocos y parió la abuela" by emphasising the excessive amount of people involved in an activity.
"Lo sabe el ciento y la madre".
"No se podía andar por la tienda. Estaba comprando el ciento y la madre allí".
"Antes de que te des cuenta ya lo sabrá todo el ciento y la madre".